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ui/webui/resources/js/util.js

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // <include src="assert.js">
 
 /**
  * Alias for document.getElementById. Found elements must be HTMLElements.
  * @param {string} id The ID of the element to find.
  * @return {HTMLElement} The found element or null if not found.
@@ skipping 375 matching lines @@
 
 /**
  * Quote a string so it can be used in a regular expression.
  * @param {string} str The source string.
  * @return {string} The escaped string.
  */
 function quoteString(str) {
   return str.replace(/([\\\.\+\*\?\[\^\]\$\(\)\{\}\=\!\<\>\|\:])/g, '\\$1');
 }
 
+/**
+ * Runs |callback| first time the |eventName| event is fired on |target|, then
+ * removes the listener.
+ * @param {!EventTarget} target
+ * @param {string} eventName

[Dan Beam, 2016/09/01 01:33:13]

nit: maybe support multiple events?

... Callback is called and listening stops on the first event triggered. ...

@param {!Array<!string>|!string} eventNames An array of event types or a
space-separated list as a string (i.e. 'click mousedown').

var eventNames =
    Array.isArray(eventNames) ? eventNames : eventNames.split(/\s+/);

function removeAllAndCallback() {
  eventNames.forEach(function(eventName) {
    target.removeEventListener(eventName, removeAllAndCallback);
  });
  return callback(event);
}

eventNames.forEach(function(eventName) {
  target.addEventListener(eventName, removeAllAndCallback);
});

listenOnce(window, 'scroll resize', reposition);

[michaelpg, 2016/09/01 02:20:26]

Done. I had briefly considered this but thought it may be overkill.

+ * @param {function(!Event)} callback Called at most once. The
+ *     optional return value is passed on by the listener.
+ */
+function listenOnce(target, eventName, callback) {
+  target.addEventListener(eventName, function runOnce(event) {

[michaelpg, 2016/09/01 01:00:27]

dbeam: your example returned a Promise, but this way is more general-purpose
(and can be used synchronously when necessary)

+    target.removeEventListener(eventName, runOnce, false);

[michaelpg, 2016/09/01 01:00:27]

apparently closure requires this 3rd argument for EventTarget...

+    return callback(event);
+  }, false);

[Dan Beam, 2016/09/01 01:33:13]

we'll probably need some type @param {boolean=} opt_capture eventually, fine to
wait on that if we'd like

[michaelpg, 2016/09/01 02:20:27]

Acknowledged (does anyone actually use that? I've forgotten how it works more
often than I've used it.)

+}
+
 // <if expr="is_ios">
 // Polyfill 'key' in KeyboardEvent for iOS.
 // This function is not intended to be complete but should
 // be sufficient enough to have iOS work correctly while
 // it does not support key yet.
 if (!('key' in KeyboardEvent.prototype)) {
   Object.defineProperty(KeyboardEvent.prototype, 'key', {
     /** @this {KeyboardEvent} */
     get: function () {
       // 0-9
@@ skipping 46 matching lines @@
         case 0xdb: return '[';
         case 0xdd: return ']';
       }
       return 'Unidentified';
     }
   });
 } else {
   window.console.log("KeyboardEvent.Key polyfill not required");
 }
 // </if>  /* is_ios */