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gaia/shared/js/lazy_loader.js

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+/* exported LazyLoader */
+/* globals HtmlImports, Promise */
+'use strict';
+
+/**
+ * This contains a simple LazyLoader implementation
+ * To use:
+ *
+ *   LazyLoader.load(
+ *    ['/path/to/file.js', '/path/to/file.css', 'domNode'], callback
+ *   );
+ */
+var LazyLoader = (function() {
+
+  function LazyLoader() {
+    this._loaded = {};
+    this._isLoading = {};
+  }
+
+  LazyLoader.prototype = {
+
+    _js: function(file, callback) {
+      var script = document.createElement('script');
+      script.src = file;
+      // until bug 916255 lands async is the default so
+      // we must disable it so scripts load in the order they where
+      // required.
+      script.async = false;
+      script.addEventListener('load', callback);
+      document.head.appendChild(script);
+      this._isLoading[file] = script;
+    },
+
+    _css: function(file, callback) {
+      var style = document.createElement('link');
+      style.type = 'text/css';
+      style.rel = 'stylesheet';
+      style.href = file;
+      document.head.appendChild(style);
+      callback();
+    },
+
+    _html: function(domNode, callback) {
+
+      // The next few lines are for loading html imports in DEBUG mode
+      if (domNode.getAttribute('is')) {
+        this.load(['/shared/js/html_imports.js'], function() {
+          HtmlImports.populate(callback);
+        }.bind(this));
+        return;
+      }
+
+      for (var i = 0; i < domNode.childNodes.length; i++) {
+        if (domNode.childNodes[i].nodeType == document.COMMENT_NODE) {
+          domNode.innerHTML = domNode.childNodes[i].nodeValue;
+          break;
+        }
+      }
+
+      window.dispatchEvent(new CustomEvent('lazyload', {
+        detail: domNode
+      }));
+
+      callback();
+    },
+
+    /**
+     * Retrieves content of JSON file.
+     *
+     * @param {String} file Path to JSON file
+     * @param {Boolean} mozSystem If xhr should use mozSystem permissions
+     * @return {Promise} A promise that resolves to the JSON content
+     * or null in case of invalid path. Rejects if an error occurs.
+     */
+    getJSON: function(file, mozSystem) {
+      return new Promise(function(resolve, reject) {
+        var xhr;
+        if (mozSystem) {
+          xhr = new XMLHttpRequest({mozSystem: true});
+        } else {
+          xhr = new XMLHttpRequest();
+        }
+        xhr.open('GET', file, true);
+        xhr.responseType = 'json';
+
+        xhr.onerror = function(error) {
+          reject(error);
+        };
+        xhr.onload = function() {
+          if (xhr.response !== null) {
+            resolve(xhr.response);
+          } else {
+            reject(new Error('No valid JSON object was found (' + 
+			     xhr.status + ' ' + xhr.statusText + ')'));
+          }
+        };
+
+        xhr.send();
+      });
+    },
+
+    load: function(files, callback) {
+      var deferred = {};
+      deferred.promise = new Promise(resolve => {
+        deferred.resolve = resolve;
+      });
+
+      if (!Array.isArray(files)) {
+        files = [files];
+      }
+
+      var loadsRemaining = files.length, self = this;
+      function perFileCallback(file) {
+        if (self._isLoading[file]) {
+          delete self._isLoading[file];
+        }
+        self._loaded[file] = true;
+
+        if (--loadsRemaining === 0) {
+          deferred.resolve();
+          if (callback) {
+            callback();
+          }
+        }
+      }
+
+      for (var i = 0; i < files.length; i++) {
+        var file = files[i];
+
+        if (this._loaded[file.id || file]) {
+          perFileCallback(file);
+        } else if (this._isLoading[file]) {
+          this._isLoading[file].addEventListener(
+            'load', perFileCallback.bind(null, file));
+        } else {
+          var method, idx;
+          if (typeof file === 'string') {
+            method = file.match(/\.([^.]+)$/)[1];
+            idx = file;
+          } else {
+            method = 'html';
+            idx = file.id;
+          }
+
+          this['_' + method](file, perFileCallback.bind(null, idx));
+        }
+      }
+
+      return deferred.promise;
+    }
+  };
+
+  return new LazyLoader();
+}());