Add initial version

.gitignore

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+# distribution
+dist
+
 # Logs
 logs
 *.log

AxeObserver.js

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+import axeCore from 'axe-core'
+import debounce from 'lodash.debounce'
+
+// If requestIdleCallback is not supported, we fallback to setTimeout
+// Ref: https://developers.google.com/web/updates/2015/08/using-requestidlecallback
+const requestIdleCallback =
+  window.requestIdleCallback ||
+  function(callback) {
+    setTimeout(callback, 1)
+  }
+
+// The AxeObserver class takes a violationsCallback, which is invoked with an
+// array of observed violations.
+export default class AxeObserver {
+  constructor(
+    violationsCallback,
+    axeConfiguration = axeInstance => {
+      axeInstance.configure({
+        reporter: 'v2',
+        checks: [
+          {
+            id: 'color-contrast',
+            options: {
+              // Prevent axe from automatically scrolling
+              noScroll: true
+            }
+          }
+        ]
+      })
+    }
+  ) {
+    if (typeof violationsCallback !== 'function') {
+      throw new Error(
+        'The AxeObserver constructor requires a violationsCallback'
+      )
+    }
+
+    this._violationsCallback = violationsCallback
+
+    this.observe = this.observe.bind(this)
+    this.disconnect = this.disconnect.bind(this)
+    this._auditTargetNode = this._auditTargetNode.bind(this)
+
+    this._mutationObservers = []
+    this._alreadyReportedIncidents = new Set()
+
+    axeConfiguration(axeCore)
+  }
+  observe(targetNode, debounceMs = 1000, maxWaitMs = debounceMs * 5) {
+    if (!targetNode) {
+      throw new Error('AxeObserver.observe requires a targetNode')
+    }
+
+    const scheduleAudit = debounce(
+      () => requestIdleCallback(() => this._auditTargetNode(targetNode)),
+      debounceMs,
+      { leading: true, maxWait: maxWaitMs }
+    )
+    const mutationObserver = new window.MutationObserver(scheduleAudit)
+
+    // observe changes
+    mutationObserver.observe(targetNode, {
+      attributes: true,
+      subtree: true
+    })
+
+    this._mutationObservers.push(mutationObserver)
+
+    // run initial audit
+    scheduleAudit(targetNode)
+  }
+  disconnect() {
+    this._mutationObservers.forEach(mutationObserver => {
+      mutationObserver.disconnect()
+    })
+  }
+  async _auditTargetNode(targetNode) {
+    const response = await axeCore.run(targetNode)
+
+    const violationsToReport = response.violations.filter(violation => {
+      const filteredNodes = violation.nodes.filter(node => {
+        const key = node.target.toString() + violation.id
+
+        const wasAlreadyReported = this._alreadyReportedIncidents.has(key)
+
+        if (wasAlreadyReported) {
+          // filter out this violation for this node
+          return false
+        } else {
+          // add to alreadyReportedIncidents as we'll report it now
+          this._alreadyReportedIncidents.add(key)
+          return true
+        }
+      })
+
+      return filteredNodes.length > 0
+    })
+
+    const hasViolationsToReport = violationsToReport.length > 0
+
+    if (hasViolationsToReport) {
+      this._violationsCallback(violationsToReport)
+    }
+  }
+}

README.MD

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+# Agnostic Axe
+
+Test your web application with the [axe-core](https://github.com/dequelabs/axe-core) accessibility testing library. Results will show in the browser console.
+
+## Installation
+
+You can install the module from NPM.
+
+```sh
+npm install --save-dev agnostic-axe
+```
+
+## Usage
+
+```js
+import('agnostic-axe').then(({ AxeObserver, logViolations }) => {
+  const MyAxeObserver = new AxeObserver(logViolations)
+  MyAxeObserver.observe(document)
+})
+```
+
+> Be sure to only run the module in your development environment. Else your application will use more resources than necessary when in production.
+
+In the example above, once the `observe` method has been invoked, `MyAxeObserver` starts reporting accessibility defects to the browser console. It continously observes the passed node for changes. If a change has been detected, it will reanalyze the node and report any new accessibility defects.
+
+To stop observing changes, one can call the `disconnect` method.
+
+```js
+MyAxeObserver.disconnect()
+```
+
+### Configuration
+
+The `AxeObserver` constructor takes two parameters:
+
+- `violationsCallback` (required). A function that is invoked with an array of violations, as reported by [axe-core](https://github.com/dequelabs/axe-core). To log violations to the console, simply pass the `logViolations` function exported by this module.
+- `axeConfiguration` (optional). A function that is invoked with the instance of [axe-core](https://github.com/dequelabs/axe-core) used by module. It can be used to [configure axe-core](https://github.com/dequelabs/axe-core/blob/develop/doc/API.md#api-name-axeconfigure). See the source code for the default configuration used.
+
+The `AxeObserver.observe` method takes two parameters:
+
+- `targetNode` (required). The node that should be observed & analyzed.
+- `debounceMs` (optional, defaults to `1000`). The number of milliseconds that updates should cease before an analysis is performed.
+- `maxWaitMs` (optional, defaults to `debounceMs * 5`). Number of milliseconds after which an analysis will be performed, even if the targetNode is still updating.
+
+## Credits
+
+Agnostic axe itself is merely a wrapper around [axe-core](https://github.com/dequelabs/axe-core) that employs a `MutationObserver` to detect DOM changes automatically. Most of its logic for formatting violations return by [axe-core](https://github.com/dequelabs/axe-core) is taken from [react-axe](https://github.com/dequelabs/react-axe).

index.js

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+import AxeObserver from './AxeObserver.js'
+import logViolations from './logViolations.js'
+
+export default { AxeObserver, logViolations }

logViolations.js

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+import axeCore from 'axe-core'
+
+const boldCourier = 'font-weight:bold;font-family:Courier;'
+const critical = 'color:red;font-weight:bold;'
+const serious = 'color:red;font-weight:normal;'
+const moderate = 'color:orange;font-weight:bold;'
+const minor = 'color:orange;font-weight:normal;'
+const defaultReset = 'font-color:black;font-weight:normal;'
+
+// The logViolations function takes an array of violations and logs them to the
+// console in a nice format. Its code is copied from the `react-axe` module.
+// Ref: https://github.com/dequelabs/react-axe
+export default function logViolations(violations) {
+  if (violations.length) {
+    console.group('%cNew aXe issues', serious)
+    violations.forEach(function(result) {
+      var fmt
+      switch (result.impact) {
+        case 'critical':
+          fmt = critical
+          break
+        case 'serious':
+          fmt = serious
+          break
+        case 'moderate':
+          fmt = moderate
+          break
+        case 'minor':
+          fmt = minor
+          break
+        default:
+          fmt = minor
+          break
+      }
+      console.groupCollapsed(
+        '%c%s: %c%s %s',
+        fmt,
+        result.impact,
+        defaultReset,
+        result.help,
+        result.helpUrl
+      )
+      result.nodes.forEach(function(node) {
+        failureSummary(node, 'any')
+        failureSummary(node, 'none')
+      })
+      console.groupEnd()
+    })
+    console.groupEnd()
+  }
+}
+
+function logElement(node, logFn) {
+  var el = document.querySelector(node.target.toString())
+  if (!el) {
+    logFn('Selector: %c%s', boldCourier, node.target.toString())
+  } else {
+    logFn('Element: %o', el)
+  }
+}
+
+function logHtml(node) {
+  console.log('HTML: %c%s', boldCourier, node.html)
+}
+
+function logFailureMessage(node, key) {
+  var message = axeCore._audit.data.failureSummaries[key].failureMessage(
+    node[key].map(function(check) {
+      return check.message || ''
+    })
+  )
+
+  console.error(message)
+}
+
+function failureSummary(node, key) {
+  if (node[key].length > 0) {
+    logElement(node, console.groupCollapsed)
+    logHtml(node)
+    logFailureMessage(node, key)
+
+    var relatedNodes = []
+    node[key].forEach(function(check) {
+      relatedNodes = relatedNodes.concat(check.relatedNodes)
+    })
+
+    if (relatedNodes.length > 0) {
+      console.groupCollapsed('Related nodes')
+      relatedNodes.forEach(function(relatedNode) {
+        logElement(relatedNode, console.log)
+        logHtml(relatedNode)
+      })
+      console.groupEnd()
+    }
+
+    console.groupEnd()
+  }
+}