Language settings: Fix unnecessarily shown move buttons

chrome/browser/resources/settings/languages_page/languages_page.js

 // Copyright 2015 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.
 
 /**
  * @fileoverview 'settings-languages-page' is the settings page
  * for language and input method settings.
  */
 cr.exportPath('settings');
 
@@ skipping 74 matching lines @@
     this.showAddLanguagesDialog_ = true;
     this.async(function() {
       var dialog = this.$$('settings-add-languages-dialog');
       dialog.addEventListener('close', function() {
         this.showAddLanguagesDialog_ = false;
       }.bind(this));
     });
   },
 
   /**
+   * @param {number} n
+   * @param {!LanguageState} language
+   * @return {boolean} True if |language| is at the |n|th index in the list of
+   *     enabled languages. Used to show or hide the "Move" buttons for ordering
+   *     preferred languages.

[stevenjb, 2017/02/02 00:26:34]

nit: Put 'Used to show or hide...' at top of comment.

[michaelpg, 2017/02/02 19:38:36]

Done.

+   * @private
+   */
+  isNthLanguage_: function(n, language) {
+    var compareLanguage = assert(this.languages.enabled[n]);
+    return language.language == compareLanguage.language;
+  },
+
+  /**
    * @param {!LanguageState} language
-   * @return {boolean} True if |language| is first in the list of enabled
-   *     languages. Used to hide the "Move up" option.
+   * @return {boolean} True if the "Move to top" option for |language| should be
+   *     visible.
    * @private
    */
-  isFirstLanguage_: function(language) {
-    return language == this.languages.enabled[0];
+  showMoveUp_: function(language) {
+    // "Move up" is a no-op for the top language, and redundant with
+    // "Move to top" for the 2nd language.
+    return !this.isNthLanguage_(0, language) &&
+           !this.isNthLanguage_(1, language);
   },
 
   /**
    * @param {!LanguageState} language
-   * @return {boolean} True if |language| is first or second in the list of
-   *     enabled languages. Used to hide the "Move to top" option.
+   * @return {boolean} True if the "Move down" option for |language| should be
+   *     visible.
    * @private
    */
-  isFirstOrSecondLanguage_: function(language) {
-    return this.languages.enabled.slice(0, 2).includes(language);
+  showMoveDown_: function(language) {
+    return !this.isNthLanguage_(this.languages.enabled.length - 1, language);
   },
 
   /**
-   * @param {!LanguageState} language
-   * @return {boolean} True if |language| is last in the list of enabled
-   *     languages. Used to hide the "Move down" option.
-   * @private
-   */
-  isLastLanguage_: function(language) {
-    return language == this.languages.enabled.slice(-1)[0];
-  },
-
-  /**
    * @param {!Object} change Polymer change object for languages.enabled.*.
    * @return {boolean} True if there are less than 2 languages.
    */
   isHelpTextHidden_: function(change) {
     return this.languages.enabled.length <= 1;
   },
 
   /**
    * @param {!LanguageState} languageState
    * @param {string} prospectiveUILanguage The chosen UI language.
@@ skipping 402 matching lines @@
     if (e.target.tagName == expandButtonTag)
       return;
 
     /** @type {!CrExpandButtonElement} */
     var expandButton = e.currentTarget.querySelector(expandButtonTag);
     assert(expandButton);
     expandButton.expanded = !expandButton.expanded;
   },
 });
 })();