# Axe JavaScript Accessibility API

## Table of Contents

1. [Section 1: Introduction](#section-1-introduction)
   1. [Get Started](#getting-started)
1. [Section 2: API Reference](#section-2-api-reference)
   1. [Overview](#overview)
   1. [API Notes](#api-notes)
   1. [API Name: axe.getRules](#api-name-axegetrules)
   1. [API Name: axe.configure](#api-name-axeconfigure)
   1. [API Name: axe.reset](#api-name-axereset)
   1. [API Name: axe.run](#api-name-axerun)
      1. [Parameters axe.run](#parameters-axerun)
         1. [Context Parameter](#context-parameter)
         2. [Options Parameter](#options-parameter)
         3. [Callback Parameter](#callback-parameter)
      1. [Return Promise](#return-promise)
      1. [Error result](#error-result)
      1. [Results Object](#results-object)
   1. [API Name: axe.registerPlugin](#api-name-axeregisterplugin)
   1. [API Name: axe.cleanup](#api-name-axecleanup)
   1. [API Name: axe.setup](#api-name-axesetup)
   1. [API Name: axe.teardown](#api-name-axeteardown)
   1. [API Name: axe.frameMessenger](#api-name-axeframemessenger)
   1. [API name: axe.runPartial / axe.finishRun](#api-name-axerunpartial--axefinishrun)
   1. [Virtual DOM Utilities](#virtual-dom-utilities)
      1. [API Name: axe.utils.querySelectorAll](#api-name-axeutilsqueryselectorall)
      1. [API Name: axe.utils.getRule](#api-name-axeutilsgetrule)
   1. [Common Functions](#common-functions)
1. [Section 3: Example Reference](#section-3-example-reference)
1. [Section 4: Performance](#section-4-performance)

## Section 1: Introduction

The axe API is designed to be an improvement over the previous generation of accessibility APIs. It provides the following benefits:

- Runs in any modern browser
- Designed to work with existing testing infrastructure
- Runs locally, no connection to a third-party server is necessary
- Performs violation checking on multiple levels of nested iframes
- Provides list of rules and elements that passed accessibility checking, ensuring rules have been run against entire document
- Only checks rendered content to minimize false positives (that includes visually-hidden content)

### Getting Started

This section gives a quick description of how to use the axe APIs to analyze web page content and return a JSON object that lists any accessibility violations found.

The axe API can be used as part of a broader process that is performed on many, if not all, pages of a website. The API is used to analyze web page content and return a JSON object that lists any accessibility violations found. Here is how to get started:

1. Load page in testing system
2. Optionally, set configuration options for the JavaScript API (`axe.configure`)
3. Call analyze JavaScript API (`axe.run`)
4. Either assert against results or save them for later processing
5. Repeat for any inactive or non-rendered content after making it visible

## Section 2: API Reference

### Overview

The axe APIs are provided in the JavaScript file axe.js. It must be included in the web page under test, as well as each `iframe` under test. Parameters are sent as JavaScript function parameters. Results are returned in JSON format.

### Full API Reference for Developers

For a full listing of API offered by axe, clone the repository and run `npm run api-docs`. This generates `jsdoc` documentation under `doc/api` which can be viewed using the browser.

### API Notes

- A Rule test is made up of sub-tests. Each sub-test is returned in an array of 'checks'
- The `"helpUrl"` in the results object is a link to a broader description of the accessibility issue and suggested remediation. These links point to Deque University help pages, which do not require a login.
- Axe does not test hidden regions, such as inactive menus or modal windows. To test those for accessibility, write tests that activate or render the regions visible and run the analysis again.

### Axe-core Tags

Each rule in axe-core has a number of tags. These provide metadata about the rule. Each rule has one tag that indicates which WCAG version / level it belongs to, or if it doesn't, it has the `best-practice` tag. If the rule is required by WCAG, there is a tag that references the success criterion number. For example, the `wcag111` tag means a rule is required for WCAG 2 success criterion 1.1.1.

The `experimental`, `ACT`, `TT`, and `section508` tags are only added to some rules. Each rule with a `section508` tag also has a tag to indicate what requirement in old Section 508 the rule is required by. For example `section508.22.a`.

| Tag Name          | Accessibility Standard / Purpose                                                                                              |
| ----------------- | ----------------------------------------------------------------------------------------------------------------------------- |
| `wcag2a`          | WCAG 2.0 Level A                                                                                                              |
| `wcag2aa`         | WCAG 2.0 Level AA                                                                                                             |
| `wcag2aaa`        | WCAG 2.0 Level AAA                                                                                                            |
| `wcag21a`         | WCAG 2.1 Level A                                                                                                              |
| `wcag21aa`        | WCAG 2.1 Level AA                                                                                                             |
| `wcag22aa`        | WCAG 2.2 Level AA                                                                                                             |
| `best-practice`   | Common accessibility best practices                                                                                           |
| `wcag2a-obsolete` | WCAG 2.0 Level A, no longer required for conformance                                                                          |
| `wcag***`         | WCAG success criterion e.g. wcag111 maps to SC 1.1.1                                                                          |
| `ACT`             | W3C approved Accessibility Conformance Testing rules                                                                          |
| `section508`      | Old Section 508 rules                                                                                                         |
| `section508.*.*`  | Requirement in old Section 508                                                                                                |
| `TTv5`            | Trusted Tester v5 rules                                                                                                       |
| `TT*.*`           | Test ID in Trusted Tester                                                                                                     |
| `EN-301-549`      | Rule required under [EN 301 549](https://www.etsi.org/deliver/etsi_en/301500_301599/301549/03.02.01_60/en_301549v030201p.pdf) |
| `EN-9.*`          | Section in EN 301 549 listing the requirement                                                                                 |
| `RGAAv4`          | Rule required under [RGAA](https://accessibilite.numerique.gouv.fr/methode/criteres-et-tests/)                                |
| `RGAA-*.*.*`      | Section in RGAA listing the requirement                                                                                       |
| `experimental`    | Cutting-edge rules, disabled by default                                                                                       |
| `cat.*`           | Category mappings used by Deque (see below)                                                                                   |

All rules have a `cat.*` tag, which indicates what type of content it is part of. The following `cat.*` tags exist in axe-core:

| Category name                 |
| ----------------------------- |
| `cat.aria`                    |
| `cat.color`                   |
| `cat.forms`                   |
| `cat.keyboard`                |
| `cat.language`                |
| `cat.name-role-value`         |
| `cat.parsing`                 |
| `cat.semantics`               |
| `cat.sensory-and-visual-cues` |
| `cat.structure`               |
| `cat.tables`                  |
| `cat.text-alternatives`       |
| `cat.time-and-media`          |

### API Name: axe.getRules

#### Purpose

To get information on all the rules in the system.

#### Description

Returns a list of all rules with their ID and description

#### Synopsis

`axe.getRules([Tag Name 1, Tag Name 2...]);`

#### Parameters

- `tags` - **optional** Array of tags used to filter returned rules. If omitted, it will return all rules. See [axe-core tags](#axe-core-tags).

**Returns:** Array of rules that match the input filter with each entry having a format of `{ruleId: <id>, description: <desc>, helpUrl: <url>, help: <help>, tags: <tags>}`

#### Example 1

In this example, we pass in the WCAG 2 A and AA tags into `axe.getRules` to retrieve only those rules. The function call returns an array of rules.

**Call:** `axe.getRules(['wcag2aa', 'wcag2a']);`

**Returned Data:**

```js
[
  {
    description: "Ensure <area> elements of image maps have alternate text",
    help: "Active <area> elements must have alternate text",
    helpUrl: "https://dequeuniversity.com/rules/axe/3.5/area-alt?application=axeAPI",
    ruleId: "area-alt",
    tags: [
      "cat.text-alternatives",
      "wcag2a",
      "wcag111",
      "wcag244",
      "wcag412",
      "section508",
      "section508.22.a"
    ],
    actIds: ['c487ae']
  },
  {
    description: "Ensure ARIA attributes are allowed for an element's role",
    help: "Elements must only use allowed ARIA attributes",
    helpUrl: "https://dequeuniversity.com/rules/axe/3.5/aria-allowed-attr?application=axeAPI",
    ruleId: "aria-allowed-attr",
    tags: [
      "cat.aria",
      "wcag2a",
      "wcag412"
    ]
  }
  …
]
```

### API Name: axe.configure

#### Purpose

To configure the format of the data used by axe. This can be used to add new rules, which must be registered with the library to execute.

**Important**: `axe.configure()` does not communicate configuration calls into iframes. Instead `axe.configure()` must be called with the same argument in each `frame` / `iframe` individually.

#### Description

User specifies the format of the JSON structure passed to the callback of `axe.run`

#### Synopsis

```js
axe.configure({
  branding: String,
  reporter: 'option' | Function,
  checks: [Object],
  rules: [Object],
  standards: Object,
  locale: Object,
  axeVersion: String,
  disableOtherRules: Boolean,
  noHtml: Boolean
});
```

#### Parameters

- `configurationOptions` - Options object; where the valid name, value pairs are:
  - `branding` - mixed(optional) Used to set the branding of the helpUrls
    - `brand` - string(optional) sets the brand string - default "axe"
    - `application` - string(optional) sets the application string - default "axeAPI"
  - `reporter` - Used to set the output format that the axe.run function will pass to the callback function. Can pass a reporter name or a custom reporter function. Valid names are:
    - `v1` to use the previous version's format: `axe.configure({ reporter: "v1" });`
    - `v2` to use the current version's format: `axe.configure({ reporter: "v2" });`
    - `raw` to return the raw result data without formatting: `axe.configure({ reporter: "raw" });`
    - `raw-env` to return the raw result data with environment data: `axe.configure({ reporter: "raw-env" });`
    - `no-passes` to return only violation results: `axe.configure({ reporter: "no-passes" });`
  - `checks` - Used to add checks to the list of checks used by rules, or to override the properties of existing checks
    - The checks attribute is an array of check objects
    - Each check object can contain the following attributes
      - `id` - string(required). This uniquely identifies the check. If the check already exists, this will result in any supplied check properties being overridden. The properties below that are marked required if new are optional when the check is being overridden.
      - `evaluate` - string(required for new). The ID of the function that implements the check's functionality. See the [`metadata-function-map`](../lib/core/base/metadata-function-map.js) file for all defined IDs.
      - `after` - string(optional). The ID of the function that gets called for checks that operate on a page-level basis, to process the results from the iframes.
      - `options` - mixed(optional). This is the options structure that is passed to the evaluate function and is intended to be used to configure checks. It is the most common property that is intended to be overridden for existing checks.
      - `enabled` - boolean(optional, default `true`). This is used to indicate whether the check is on or off by default. Checks that are off are not evaluated, even when included in a rule. Overriding this is a common way to disable a particular check across multiple rules.
  - `rules` - Used to add rules to the existing set of rules, or to override the properties of existing rules
    - The rules attribute is an Array of rule objects
    - each rule object can contain the following attributes
      - `id` - string(required). This uniquely identifies the rule. If the rule already exists, it will be overridden with any of the attributes supplied. The attributes below that are marked required, are only required for new rules.
      - `impact` - string(required). Sets the impact of that rule's results
      - `reviewOnFail` - boolean(option, default `false`). Override the result of a rule to return "Needs Review" rather than "Violation" if the rule fails.
      - `selector` - string(optional, default `*`). A [CSS selector](./developer-guide.md#supported-css-selectors) used to identify the elements that are passed into the rule for evaluation.
      - `excludeHidden` - boolean(optional, default `true`). This indicates whether elements that are hidden from all users are to be passed into the rule for evaluation.
      - `enabled` - boolean(optional, default `true`). Whether the rule is turned on. This is a common attribute for overriding.
      - `pageLevel` - boolean(optional, default `false`). When set to true, this rule is only applied when the entire page is tested. Results from nodes on different frames are combined into a single result. See [page level rules](#page-level-rules).
      - `any` - array(optional, default `[]`). This is a list of checks that, if none "pass", will generate a violation.
      - `all` - array(optional, default `[]`). This is a list of checks that, if any "fails", will generate a violation.
      - `none` - array(optional, default `[]`). This is a list of checks that, if any "pass", will generate a violation.
      - `tags` - array(optional, default `[]`). A list if the tags that "classify" the rule. See [axe-core tags](#axe-core-tags).
      - `matches` - string(optional). The ID of the filtering function that will exclude elements that match the `selector` property. See the [`metadata-function-map`](../lib/core/base/metadata-function-map.js) file for all defined IDs.
  - `standards` - object(optional). Used to configure the standards object. See the [Standards Object docs](./standards-object.md) for the structure of each standards object.
  - `disableOtherRules` - Disables all rules not included in the `rules` property.
  - `locale` - A locale object to apply (at runtime) to all rules and checks, in the same shape as `/locales/*.json`.
  - `axeVersion` - Set the compatible version of a custom rule with the current axe version. Compatible versions are all patch and minor updates that are the same as, or newer than those of the `axeVersion` property.
  - `noHtml` - Disables the HTML output of nodes from rules.
  - `allowedOrigins` - Set which origins (URL domains) will communicate test data with. See [allowedOrigins](#allowedorigins).

**Returns:** Nothing

**Note**: The `branding` property accepts a `string`, which sets the application. Passing it an object is deprecated as of axe-core 4.4.0, as is the `branding.brand` property.

##### Page level rules

Page level rules split their evaluation into two phases. A 'data collection' phase which is done inside the 'evaluate' function and an assessment phase which is done inside the 'after' function. The evaluate function executes inside each individual frame and is responsible for collection data that is passed into the after function which inspects that data and makes a decision.

Page level rules raise violations on the entire document and not on individual nodes or frames from which the data was collected. For an example of how this works, see the heading order check:

- [lib/checks/navigation/heading-order.json](https://github.com/dequelabs/axe-core/blob/master/lib/checks/navigation/heading-order.json)
- [lib/checks/navigation/heading-order-evaluate.js](https://github.com/dequelabs/axe-core/blob/master/lib/checks/navigation/heading-order-evaluate.js)
- [lib/checks/navigation/heading-order-after.js](https://github.com/dequelabs/axe-core/blob/master/lib/checks/navigation/heading-order-after.js)

##### allowedOrigins

Axe-core will only communicate results to frames of the same origin (the URL domain). To configure axe so that it exchanges results across different origins, you can configure allowedOrigins. This configuration must happen in **every frame**. For example:

```js
axe.configure({
  allowedOrigins: ['<same_origin>', 'https://deque.com']
});
```

The `allowedOrigins` option has two wildcard options. `<same_origin>` always corresponds to the current domain. If you want to block all frame communication, set `allowedOrigins` to `[]`. To configure axe-core to communicate to all origins, use `<unsafe_all_origins>`. **This is not recommended**. Because this is the only way to test iframes on `file://`, it is recommended to use a localhost server such as [http-server](https://www.npmjs.com/package/http-server) instead.

Use of `allowedOrigins` is not necessary if an alternative [frameMessenger](#api-name-axeframemessenger) is used.

### API Name: axe.reset

#### Purpose

Reset the configuration to the default configuration.

#### Description

Override any previous calls to `axe.configure` and restore the configuration to the default configuration. Note: this will NOT unregister any new rules or checks that were registered but will reset the configuration back to the default configuration for everything else.

#### Synopsis

```js
axe.reset();
```

#### Parameters

None

### API Name: axe.run

#### Purpose

Analyze rendered content on the currently loaded page

#### Description

Runs a number of rules against the provided HTML page and returns the resulting issue list

#### Synopsis

```js
axe.run(context, options, (err, results) => {
  // ...
});
```

#### Parameters axe.run

- [`context`](#context-parameter): (optional) Defines the scope of the analysis - the part of the DOM that you would like to analyze. This will typically be the `document` or a specific selector such as class name, ID, selector, etc.
- [`options`](#options-parameter): (optional) Set of options that change how `axe.run` works, including what rules will run. To pass options to specific checks, use `axe.configure`.
- [`callback`](#callback-parameter): (optional) The callback function which receives either null or an [error result](#error-result) as the first parameter, and the [results object](#results-object) when analysis is completed successfully, or undefined if it did not.

##### Context Parameter

By default, `axe.run` will test the entire document. The context object is an optional parameter that can be used to specify which element should and which should not be tested. It can be passed one of the following:

1. An element reference that represents the portion of the document that must be analyzed
   - Example: To limit analysis to the `<div id="content">` element: `document.getElementById("content")`
1. A NodeList such as returned by `document.querySelectorAll`.
1. A [CSS selector](./developer-guide.md#supported-css-selectors) that selects the portion(s) of the document that must be analyzed.
1. An object with `exclude` and/or `include` properties
1. An object with a `fromFrames` property
1. An object with a `fromShadowDom` property

Read [context.md](context.md) for details about the context object.

###### Context Parameter Examples

1. Test the `#navBar` and all other `nav` elements and its content.

```js
axe.run([`#navBar`, `nav`], (err, results) => {
  // ...
});
```

2. Test everything except `.ad-banner` elements.

```js
axe.run(
  {
    exclude: '.ad-banner'
  },
  (err, results) => {
    // ...
  }
);
```

3. Test the `form` element inside the `#payment` iframe.

```js
axe.run(
  {
    fromFrames: ['iframe#payment', 'form']
  },
  (err, results) => {
    // ...
  }
);
```

4. Exclude all `.commentBody` elements in each `.commentsShadowHost` shadow DOM tree.

```js
axe.run(
  {
    exclude: {
      fromShadowDom: ['.commentsShadowHost', '.commentBody']
    }
  },
  (err, results) => {
    // ...
  }
);
```

More details on how to use the context object are described in [context.md](context.md).

##### Options Parameter

The options parameter is flexible way to configure how `axe.run` operates. The different modes of operation are:

- Run all rules corresponding to one of the accessibility standards
- Run all rules defined in the system, except for the list of rules specified
- Run a specific set of rules provided as a list of rule ids

Additionally, there are a number or properties that allow configuration of different options:

| Property           | Default | Description                                                                                                                             |
| ------------------ | :------ | :-------------------------------------------------------------------------------------------------------------------------------------- |
| `runOnly`          | n/a     | Limit which rules are executed, based on names or tags                                                                                  |
| `rules`            | n/a     | Enable or disable rules using the `enabled` property                                                                                    |
| `reporter`         | `v1`    | Which reporter to use (see [Configuration](#api-name-axeconfigure))                                                                     |
| `resultTypes`      | n/a     | Limit which result types are processed and aggregated                                                                                   |
| `selectors`        | `true`  | Return CSS selector for elements, optimised for readability                                                                             |
| `ancestry`         | `false` | Return CSS selector for elements, with all the element's ancestors                                                                      |
| `xpath`            | `false` | Return xpath selectors for elements                                                                                                     |
| `absolutePaths`    | `false` | Use absolute paths when creating element selectors                                                                                      |
| `iframes`          | `true`  | Tell axe to run inside iframes                                                                                                          |
| `elementRef`       | `false` | Return element references in addition to the target                                                                                     |
| `frameWaitTime`    | `60000` | How long (in milliseconds) axe waits for a response from embedded frames before timing out                                              |
| `preload`          | `true`  | Any additional assets (eg: cssom) to preload before running rules. [See here for configuration details](#preload-configuration-details) |
| `performanceTimer` | `false` | Log rule performance metrics to the console                                                                                             |
| `pingWaitTime`     | `500`   | Time before axe-core considers a frame unresponsive. [See frame messenger for details](frame-messenger.md)                              |

###### Options Parameter Examples

1. Run only Rules for an accessibility standard. See [axe-core tags](#axe-core-tags).

To run only WCAG 2.0 Level A rules, specify `options` as:

```js
axe.run(
  {
    runOnly: {
      type: 'tag',
      values: ['wcag2a']
    }
  },
  (err, results) => {
    // ...
  }
);
```

To run both WCAG 2.0 Level A and Level AA rules, you must specify both `wcag2a` and `wcag2aa`:

```js
axe.run(
  {
    runOnly: {
      type: 'tag',
      values: ['wcag2a', 'wcag2aa']
    }
  },
  (err, results) => {
    // ...
  }
);
```

Alternatively, runOnly can be passed an array of tags:

```js
axe.run(
  {
    runOnly: ['wcag2a', 'wcag2aa']
  },
  (err, results) => {
    // ...
  }
);
```

If you want to specify just one tag, you can pass in a string.

```js
axe.run(
  {
    runOnly: 'wcag2a'
  },
  (err, results) => {
    // ...
  }
);
```

2. Run only a specified list of Rules

If you only want to run certain rules, specify options as:

```js
axe.run(
  {
    runOnly: {
      type: 'rule',
      values: ['ruleId1', 'ruleId2', 'ruleId3']
    }
  },
  (err, results) => {
    // ...
  }
);
```

This example will only run the rules with the id of `ruleId1`, `ruleId2`, and `ruleId3`. No other rule will run.

Alternatively, runOnly can be passed an array of rules:

```js
axe.run({
  runOnly: ['ruleId1', 'ruleId2', 'ruleId3'];
}, (err, results) => {
  // ...
})
```

If you want to specify just one rule, you can pass in a string.

```js
axe.run(
  {
    runOnly: 'ruleId1'
  },
  (err, results) => {
    // ...
  }
);
```

3. Run all enabled Rules except for a list of rules

The default operation for axe.run is to run all rules except for rules with the "experimental" tag. If certain rules should be disabled from being run, specify `options` as:

```js
axe.run(
  {
    rules: {
      'color-contrast': { enabled: false },
      'valid-lang': { enabled: false }
    }
  },
  (err, results) => {
    // ...
  }
);
```

This example will disable the rules with the id of `color-contrast` and `valid-lang`. All other rules will run. The list of valid rule IDs is specified in the section below.

4. Run a modified set or rules using tags and rule enable

By combining runOnly with type: tags and the rules option, a modified set can be defined. This lets you include rules with unspecified tags, and exclude rules that do have the specified tag(s).

```js
axe.run(
  {
    runOnly: {
      type: 'tag',
      values: ['wcag2a']
    },
    rules: {
      'color-contrast': { enabled: true },
      'valid-lang': { enabled: false }
    }
  },
  (err, results) => {
    // ...
  }
);
```

This example includes all level A rules except for valid-lang, and in addition will include the level AA color-contrast rule.

6. Only process certain types of results

The `resultTypes` option can be used to limit the number of nodes for a rule to a maximum of one. This can be useful for improving performance on very large or complicated pages when you are only interested in certain types of results.

After axe has processed all rules normally, it generates a unique selector for all nodes in all rules. This process can be time consuming, especially for pages with lots of nodes. By limiting the nodes to a maximum of one for result types you are not interested in, you can greatly speed up the tail end performance of axe.

Types listed in this option will cause rules that fall under those types to show all nodes. Types _not_ listed will cause rules that fall under one of the missing types to show a maximum of one node. This allows you to still see those results and inform the user of them if appropriate.

```js
axe.run(
  {
    resultTypes: ['violations', 'incomplete', 'inapplicable']
  },
  (err, results) => {
    // ...
  }
);
```

This example will return all the nodes for all rules that fall under the "violations", "incomplete", and "inapplicable" result types. Since the "passes" type was not specified, it will return at most one node for each rule that passes.

###### <a id='preload-configuration-details'></a> Preload Configuration in Options Parameter

The `preload` attribute (defaults to `true`) in options parameter, accepts a `boolean` or an `object` where an array of assets can be specified.

1. Specifying a `boolean`

```js
axe.run(
  {
    preload: true
  },
  (err, results) => {
    // ...
  }
);
```

2. Specifying an `object`

```js
axe.run(
  {
    preload: { assets: ['cssom'], timeout: 50000 }
  },
  (err, results) => {
    // ...
  }
);
```

The `assets` attribute expects an array of preload(able) constraints to be fetched. The current set of values supported for `assets` is listed in the following table:

| Asset Type | Description                                                                                                                                                                                                                                                                                                                                                                                                                                 |
| :--------- | :------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| `cssom`    | This asset type preloads all CSS Stylesheets rulesets specified in the page. The stylesheets can be an external cross-domain resource, a relative stylesheet or an inline style with in the head tag of the document. If the stylesheet is an external cross-domain a network request is made. An object representing the CSS Rules from each stylesheet is made available to the checks evaluate function as `preloadedAssets` at run-time |
| `media`    | This asset type preloads metadata information of any HTMLMediaElement in the specified document                                                                                                                                                                                                                                                                                                                                             |

The `timeout` attribute in the object configuration is `optional` and has a fallback default value (10000ms). The `timeout` is essential for any network dependent assets that are preloaded, where-in if a given request takes longer than the specified/ default value, the operation is aborted.

Preloading is not applicable to all rules. Even if the `preload` option is enabled, preloading steps may be skipped if no enabled rules require preloading.

##### Callback Parameter

The callback parameter is a function that will be called when the asynchronous `axe.run` function completes. The callback function is passed two parameters. The first parameter will be an error thrown inside of axe if axe.run could not complete. If axe completed correctly the first parameter will be null, and the second parameter will be the results object.

#### Return Promise

If the callback was not defined, axe will return a Promise instead. Axe does not polyfill a Promise library however. So on systems without support for Promises this feature is not available. If you are unsure if the systems you will need axe on has Promise support we suggest you use the callback provided by axe.run instead.

#### Error Result

This will either be null or an object which is an instance of Error. If you are consistently receiving errors, please report this issue on the [Github issues list of Axe](https://github.com/dequelabs/axe-core/issues).

#### Results Object

The callback function passed in as the third parameter of `axe.run` runs on the results object. This object has four components – a `passes` array, a `violations` array, an `incomplete` array and an `inapplicable` array.

The `passes` array keeps track of all the passed tests, along with detailed information on each one. This leads to more efficient testing, especially when used in conjunction with manual testing, as the user can easily find out what tests have already been passed.

Similarly, the `violations` array keeps track of all the failed tests, along with detailed information on each one.

The `incomplete` array (also referred to as the "review items") indicates which nodes could neither be determined to definitively pass or definitively fail. They are separated out in order that a user interface can display these to the user for manual review (hence the term "review items").

The `inapplicable` array lists all the rules for which no matching elements were found on the page.

###### `url`

The URL of the page that was tested.

###### `timestamp`

The date and time that analysis was completed.

###### `testEngine`

The application and version that ran the audit.

###### `testEnvironment`

Information about the current browser or node application that ran the audit.

###### result arrays

The results of axe are grouped according to their outcome into the following arrays:

- `passes`: These results indicate what elements passed the rules
- `violations`: These results indicate what elements failed the rules
- `inapplicable`: These results indicate which rules did not run because no matching content was found on the page. For example, with no video, those rules won't run.
- `incomplete`: Also known as "needs review," these results were aborted and require further testing. This can happen either because of technical restrictions to what the rule can test, or because a JavaScript error occurred.

Each object returned in these arrays have the following properties:

- `description` - Text string that describes what the rule does
- `help` - Help text that describes the test that was performed
- `helpUrl` - URL that provides more information about the specifics of the violation. Links to a page on the Deque University site.
- `id` - Unique identifier for the rule; [see the list of rules](rule-descriptions.md)
- `impact` - How serious the violation is. Can be one of "minor", "moderate", "serious", or "critical" if the Rule failed or `null` if the check passed
- `tags` - Array of tags that this rule is assigned. These tags can be used in the option structure to select which rules are run ([see `axe.run` parameters for more information](#parameters-axerun)).
- `nodes` - Array of all elements the Rule tested
  - `html` - Snippet of HTML of the Element
  - `impact` - How serious the violation is. Can be one of "minor", "moderate", "serious", or "critical" if the test failed or `null` if the check passed
  - `target` - Array of either strings or Arrays of strings. If the item in the array is a string, then it is a CSS selector. If there are multiple items in the array each item corresponds to one level of iframe or frame. If there is one iframe or frame, there should be two entries in `target`. If there are three iframe levels, there should be four entries in `target`. If the item in the Array is an Array of strings, then it points to an element in a shadow DOM and each item (except the n-1th) in this array is a selector to a DOM element with a shadow DOM. The last element in the array points to the final shadow DOM node.
  - `any` - Array of checks that were made where at least one must have passed. Each entry in the array contains:
    - `id` - Unique identifier for this check. Check ids may be the same as Rule ids
    - `impact` - How serious this particular check is. Can be one of "minor", "moderate", "serious", or "critical". Each check that is part of a rule can have different impacts. The highest impact of all the checks that fail is reported for the rule
    - `message` - Description of why this check passed or failed
    - `data` - Additional information that is specific to the type of Check which is optional. For example, a color contrast check would include the foreground color, background color, contrast ratio, etc.
    - `relatedNodes` - Optional array of information about other nodes that are related to this check. For example, a duplicate id check violation would list the other selectors that had this same duplicate id. Each entry in the array contains the following information:
      - `target` - Array of selectors for the related node
      - `html` - HTML source of the related node
  - `all` - Array of checks that were made where all must have passed. Each entry in the array contains the same information as the 'any' array
  - `none` - Array of checks that were made where all must have not passed. Each entry in the array contains the same information as the 'any' array

#### Example 2

In this example, we will pass the selector for the entire document, pass no options, which means all enabled rules will be run, and have a simple callback function that logs the entire results object to the console log:

```js
axe.run(document, function (err, results) {
  if (err) throw err;
  console.log(results);
});
```

###### `passes`

- `passes[0]`
  ...
  - `help` - `"Elements must have sufficient color contrast"`
  - `helpUrl` - `"https://dequeuniversity.com/courses/html-css/visual-layout/color-contrast"`
  - `id` - `"color-contrast"`
    - `nodes`
      - `target[0]` - `"#js_off-canvas-wrap > .inner-wrap >.kinja-title.proxima.js_kinja-title-desktop"`

- `passes[1]`
  ...

###### `violations`

- `violations[0]`
  - `help` - `"<button> elements must have alternate text"`
  - `helpUrl` - `"https://dequeuniversity.com/courses/html-css/forms/form-labels#id84_example_button"`
  - `id` - `"button-name"`
    - `nodes`
      - `target[0]` - `"post_5919997 > .row.content-wrapper > .column > span > iframe"`
      - `target[1]` - `"#u_0_1 > .pluginConnectButton > .pluginButtonImage > button"`

- `violations[1]` ...

##### `passes` Results Array

In the example above, the `passes` array contains two entries that correspond to the two rules tested. The first element in the array describes a color contrast check. It relays the information that a list of nodes was checked and subsequently passed. The `help`, `helpUrl`, and `id` fields are returned as expected for each of the entries in the `passes` array. The `target` array has one element in it with a value of

`#js_off-canvas-wrap > .inner-wrap >.kinja-title.proxima.js_kinja-title-desktop`

This indicates that the element selected by the entry in `target[0]` was checked for the color contrast rule and that it passed the test.

Each subsequent entry in the passes array has the same format, but will detail the different rules that were run as part of this call to `axe.run()`.

##### `violations` Results Array

The array of `violations` contains one entry; this entry describes a test that check if buttons have valid alternate text (button-name). This first entry in the array has the `help`, `helpUrl` and `id` fields returned as expected.

The `target` array demonstrates how we specify the selectors when the node specified is inside of an `iframe` or `frame`. The first element in the `target` array - `target[0]` - specifies the selector to the `iframe` that contains the button. The second element in the `target` array - `target[1]` - specifies the selector to the actual button, but starting from inside the iframe selected in `target[0]`.

Each subsequent entry in the violations array has the same format, but will detail the different rules that were run that generated accessibility violations as part of this call to `axe.run()`.

#### Example 3

In this example, we pass the selector for the entire document, enable two additional experimental rules, and have a simple callback function that logs the entire results object to the console log:

```js
axe.run(
  document,
  {
    rules: {
      'link-in-text-block': { enabled: true },
      'p-as-heading': { enabled: true }
    }
  },
  function (err, results) {
    if (err) throw err;
    console.log(results);
  }
);
```

#### Example 4

This example shows a result object that points to an open shadow DOM element.

##### `violations[0]`

```json
{
  "help": "Elements must have sufficient color contrast",
  "helpUrl": "https://dequeuniversity.com/rules/axe/2.1/color-contrast?application=axeAPI",
  "id": "color-contrast",
  "nodes": [
    {
      "target": [["header > aria-menu", "li.expanded"]]
    }
  ]
}
```

As you can see the `target` array contains one item that is an array. This array contains two items, the first is a CSS selector string that finds the custom element `<aria-menu>` in the `<header>`. The second item in this array is the selector within that custom element's shadow DOM to find the `<li>` element with a class of `expanded`.

### API Name: axe.registerPlugin

Register a plugin with the axe plugin system. See [implementing a plugin](plugins.md) for more information on the plugin system

### API Name: axe.cleanup

Call each plugin's cleanup function. See [implementing a plugin](plugins.md).

The signature is:

```js
axe.cleanup(resolve, reject);
```

`resolve` and `reject` are functions that will be invoked on success or failure respectively.

`resolve` takes no arguments and `reject` takes a single argument that must be a string or have a toString() method in its prototype.

### API Name: axe.setup

Setup axe-cores internal `VirtualNode` tree and other required properties required to run functions in `axe.commons`.

The signature is:

```js
axe.setup(DomNode);
```

`DomNode` - is an optional DOM node to use as the root of the `VirtualNode` tree. Default is `document.documentElement`.

### API Name: axe.teardown

Cleanup the `VirtualNode` tree and internal caches. `axe.run` will call this function at the end of the run so there's no need to call it yourself afterwards.

The signature is:

```js
axe.teardown();
```

### API Name: axe.frameMessenger

Set up an alternative communication channel between parent and child frames. By default, axe-core uses `window.postMessage()`. See [frame-messenger.md](frame-messenger.md) for details.

### API name: axe.runPartial / axe.finishRun

Run axe without frame communication. This is the recommended way to run axe in browser drivers such as Selenium and Puppeteer. See [run-partial.md](run-partial.md) for details.

### Virtual DOM Utilities

Note: If you’re writing rules or checks, you’ll have both the `node` and `virtualNode` passed in.
But if you need to query the flattened tree, the documented function below should help. See the
[developer guide](./developer-guide.md) for more information.

#### API Name: axe.utils.querySelectorAll

##### Description

A querySelectorAll implementation that works on the virtual DOM and open Shadow DOM by manually walking the flattened tree instead of relying on DOM API methods which don’t step into Shadow DOM.

Note: while there is no `axe.utils.querySelector` method, you can reproduce that behavior by accessing the first item returned in the array.

##### Synopsis

```js
axe.utils.querySelectorAll(virtualNode, 'a[href]');
```

##### Parameters

- `virtualNode` – object, the flattened DOM tree to query against. `axe._tree` is available for this purpose during an audit; see below.
- `selector` – string, the [CSS selector](./developer-guide.md#supported-css-selectors) to use as a filter. For the most part, this should work seamlessly with `document.querySelectorAll`.

##### Returns

An Array of filtered HTML nodes.

#### API Name: axe.utils.getRule

##### Description

Get an axe-core `Rule` instance by ID.

##### Synopsis

```js
axe.utils.getRule('color-contrast');
```

##### Parameters

- `ruleId` - The ID of the rule.

##### Returns

An axe-core `Rule` instance.

### Common Functions

#### axe.commons.dom.getComposedParent

Get an element's parent in the flattened tree

##### Synopsis

```js
axe.commons.dom.getComposedParent(node);
```

##### Parameters

- `element` – HTMLElement. The element for which you want to find a parent

##### Returns

A DOMNode for the parent

#### axe.commons.dom.getRootNode

Return the document or document fragment (open shadow DOM)

##### Synopsis

```js
axe.commons.dom.getRootNode(node);
```

##### Parameters

- `element` – HTMLElement. The element for which you want to find the root node

##### Returns

The top-level document or shadow DOM document fragment

## Section 3: Example Reference

This package contains examples for [jasmine](examples/jasmine), [mocha](examples/mocha), [qunit](examples/qunit), and [generating HTML from the violations array](examples/html-handlebars.md). Each of these examples is in the [doc/examples](examples) folder. In each folder, there is a README.md file which contains specific information about each example.

See [axe-webdriverjs](https://github.com/dequelabs/axe-webdriverjs#axe-webdriverjs) for selenium webdriver JavaScript examples.

## Section 4: Performance

Axe-core performs very well in general and if you are analyzing average complexity pages with the default settings, you should not need to worry about performance at all. There are some scenarios that can cause performance issues. This is the list of known issues and what you can do to mitigate and/or avoid them.

### Very large pages

Certain rules (like the color-contrast rule) look at almost every element on a page and some of these rules also perform somewhat expensive operations on these elements including looking up the hierarchy, looking at overlapping elements, calculating the computed styles etc. It also calculates a unique selector for each element in the results and also de-duplicates elements so that you do not get duplicate items in your results.

If your page is very large (in terms of the number of Elements on the page) i.e. >50K elements on the page, then you will see analysis times that run over 10s on a relatively decent CPU.

#### Use resultTypes

An approach you can take to reducing the time is use the `resultTypes` option. By calling `axe.run` with the following options, axe-core will only return the full details of the `violations` array and will only return one instance of each of the `inapplicable`, `incomplete` and `pass` arrays for each rule that has at least one of those entries. This will reduce the amount of computation that axe-core does for the unique selectors.

```js
axe.run(
  {
    resultTypes: ['violations']
  },
  (err, results) => {
    // ...
  }
);
```

### Other strategies

#### Targeted color-contrast analysis

If you are analyzing multiple pages on a single Web site or application, chances are these pages all contain the same styles. It is therefore not adding any additional information to your analysis to analyze every page for color-contrast. Choose a small number of pages that represent the totality of you styles and analyze these with color-contrast and analyze all others without it.
