fix: Prevent infinitely recursing when injecting into iframes (#66)

This patch prevents `axe-webdriverjs` from infinitely recursing when injecting `axe-core` into `<iframe>`s. I've re-written the code we use for injecting which will only recurse as deep as the number of nested `<iframe>`s on the page.

In order to keep the code "easy to read/write", I've used `async/await` rather than chaining `Promise`s together. Because we do not have a clear picture of what Node.js versions we need to support here, I've added Babel in order to ensure `async/await` works in older Nodes. It is currently setup use support Node v4.

Closes #63.

.babelrc

@@ -0,0 +1,17 @@
+{
+  "presets": [
+    ["env", {
+      "targets": {
+        "node": "4"
+      }
+    }]
+  ],
+  "plugins": [
+    ["transform-runtime", {
+      "helpers": false,
+      "polyfill": false,
+      "regenerator": true,
+      "moduleName": "babel-runtime"
+    }]
+  ]
+}

.gitignore

@@ -4,3 +4,4 @@ output
 npm-shrinkwrap.json
 .nyc_output/
 coverage/
+dist

.npmignore

@@ -1,9 +1,4 @@
 node_modules
 output
-test
-Gruntfile.js
-typings
-.editorconfig
-.travis.yml
-.gitignore
-CONTRIBUTING.md
+.nyc_output/
+coverage/

lib/axe-injector.js

@@ -0,0 +1,82 @@
+class AxeInjector {
+  constructor({ driver, config, axeSource = null }) {
+    this.driver = driver;
+    this.axeSource = axeSource || require('axe-core').source;
+    this.config = config ? JSON.stringify(config) : '';
+
+    this.didLogError = false;
+    this.errorHandler = this.errorHandler.bind(this);
+  }
+
+  // Single-shot error handler. Ensures we don't log more than once.
+  errorHandler() {
+    // We've already "warned" the user. No need to do it again (mostly for backwards compatiability)
+    if (this.didLogError) {
+      return;
+    }
+
+    this.didLogError = true;
+    // eslint-disable-next-line no-console
+    console.log('Failed to inject axe-core into one of the iframes!');
+  }
+
+  // Get axe-core source (and configuration)
+  get script() {
+    return `
+      ${this.axeSource}
+      ${this.config ? `axe.configure(${this.config})` : ''}
+      axe.configure({ branding: { application: 'webdriverjs' } })
+    `;
+  }
+
+  // Inject into the provided `frame` and its child `frames`
+  async handleFrame(frame) {
+    // Switch context to the frame and inject our `script` into it
+    await this.driver.switchTo().frame(frame);
+    await this.driver.executeScript(this.script);
+
+    // Get all of <iframe>s at this level
+    const frames = await this.driver.findElements({ tagName: 'iframe' });
+
+    // Inject into each frame. Handling errors to ensure an issue on a single frame won't stop the rest of the injections.
+    return Promise.all(
+      frames.map(childFrame =>
+        this.handleFrame(childFrame).catch(this.errorHandler)
+      )
+    );
+  }
+
+  // Inject into all frames.
+  async injectIntoAllFrames() {
+    // Ensure we're "starting" our loop at the top-most frame
+    await this.driver.switchTo().defaultContent();
+
+    // Inject the script into the top-level
+    // XXX: if this `executeScript` fails, we *want* to error, as we cannot run axe-core.
+    await this.driver.executeScript(this.script);
+
+    // Get all of <iframe>s at this level
+    const frames = await this.driver.findElements({ tagName: 'iframe' });
+
+    // Inject the script into all child frames. Handle errors to ensure we don't stop execution if we fail to inject.
+    await Promise.all(
+      frames.map(childFrame =>
+        this.handleFrame(childFrame).catch(this.errorHandler)
+      )
+    );
+
+    // Move back to the top-most frame
+    return this.driver.switchTo().defaultContent();
+  }
+
+  // Inject axe, invoking the provided callback when done
+  inject(callback) {
+    this.injectIntoAllFrames()
+      .then(() => callback())
+      // For now, we intentionally ignore errors here, as
+      // allowing them to bubble up would be a breaking change.
+      .catch(() => callback());
+  }
+}
+
+module.exports = AxeInjector;

lib/index.js

@@ -1,5 +1,5 @@
-var inject = require('./inject'),
-  normalizeContext = require('./normalize-context');
+var AxeInjector = require('./axe-injector');
+var normalizeContext = require('./normalize-context');
 
 /**
  * Constructor for chainable WebDriver API
@@ -129,7 +129,8 @@ AxeBuilder.prototype.analyze = function(callback) {
     source = this._source;
 
   return new Promise(function(resolve) {
-    inject(driver, source, config, function() {
+    var injector = new AxeInjector({ driver, axeSource: source, config });
+    injector.inject(() => {
       driver
         .executeAsyncScript(
           function(context, options, config) {