1 files changed, 87 insertions, 0 deletions
diff --git a/polygerrit-ui/app/elements/plugins/gr-attribute-helper/gr-attribute-helper.js b/polygerrit-ui/app/elements/plugins/gr-attribute-helper/gr-attribute-helper.js
new file mode 100644
index 0000000000..301c12e48a
--- /dev/null
+++ b/polygerrit-ui/app/elements/plugins/gr-attribute-helper/gr-attribute-helper.js
@@ -0,0 +1,87 @@
+// Copyright (C) 2017 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+(function(window) {
+  'use strict';
+
+  function GrAttributeHelper(element) {
+    this.element = element;
+    this._promises = {};
+  }
+
+  GrAttributeHelper.prototype._getChangedEventName = function(name) {
+    return name.replace(/([a-z])([A-Z])/g, '$1-$2').toLowerCase() + '-changed';
+  };
+
+  /**
+   * Returns true if the property is defined on wrapped element.
+   * @param {string} name
+   * @return {boolean}
+   */
+  GrAttributeHelper.prototype._elementHasProperty = function(name) {
+    return this.element[name] !== undefined;
+  };
+
+  GrAttributeHelper.prototype._reportValue = function(callback, value) {
+    try {
+      callback(value);
+    } catch (e) {
+      console.info(e);
+    }
+  };
+
+  /**
+   * Binds callback to property updates.
+   *
+   * @param {string} name Property name.
+   * @param {function(?)} callback
+   * @return {function()} Unbind function.
+   */
+  GrAttributeHelper.prototype.bind = function(name, callback) {
+    const attributeChangedEventName = this._getChangedEventName(name);
+    const changedHandler = e => this._reportValue(callback, e.detail.value);
+    const unbind = () => this.element.removeEventListener(
+        attributeChangedEventName, changedHandler);
+    this.element.addEventListener(
+        attributeChangedEventName, changedHandler);
+    if (this._elementHasProperty(name)) {
+      this._reportValue(callback, this.element[name]);
+    }
+    return unbind;
+  };
+
+  /**
+   * Get value of the property from wrapped object. Waits for the property
+   * to be initialized if it isn't defined.
+   *
+   * @param {string} name Property name.
+   * @return {!Promise<?>}
+   */
+  GrAttributeHelper.prototype.get = function(name) {
+    if (this._elementHasProperty(name)) {
+      return Promise.resolve(this.element[name]);
+    }
+    if (!this._promises[name]) {
+      let resolve;
+      const promise = new Promise(r => resolve = r);
+      const unbind = this.bind(name, value => {
+        resolve(value);
+        unbind();
+      });
+      this._promises[name] = promise;
+    }
+    return this._promises[name];
+  };
+
+  window.GrAttributeHelper = GrAttributeHelper;
+})(window);