feat(typeahead): add show-hint option

- Add support for hinting on the first match in the matches list

Closes #2570
Closes #4784

Author: chenyuzhcy

Diff for: src/typeahead/docs/demo.html

@@ -66,7 +66,7 @@ <h4>Asynchronous results</h4>
 
     <h4>Custom templates for results</h4>
     <pre>Model: {{customSelected | json}}</pre>
-    <input type="text" ng-model="customSelected" placeholder="Custom template" uib-typeahead="state as state.name for state in statesWithFlags | filter:{name:$viewValue}" typeahead-template-url="customTemplate.html" class="form-control">
+    <input type="text" ng-model="customSelected" placeholder="Custom template" uib-typeahead="state as state.name for state in statesWithFlags | filter:{name:$viewValue}" typeahead-template-url="customTemplate.html" class="form-control" typeahead-show-hint="true">
 
     <h4>Custom popup templates for typeahead's dropdown</h4>
     <pre>Model: {{customPopupSelected | json}}</pre>

Diff for: src/typeahead/docs/readme.md

@@ -82,3 +82,7 @@ The typeahead directives provide several attributes:
 * `typeahead-is-open` <i class="glyphicon glyphicon-eye-open"></i>
    _(Defaults: angular.noop)_ :
    Binding to a variable that indicates if dropdown is open
+
+* `typeahead-show-hint`
+   _(Defaults: false)_ :
+   Should input show hint that matches the first option?

Diff for: src/typeahead/test/typeahead.spec.js

@@ -967,6 +967,85 @@ describe('typeahead tests', function() {
       expect($scope.result).toEqual($scope.states[0]);
     });
   });
+  
+  describe('input hint', function() {
+    var element;
+
+    beforeEach(function() {
+      element = prepareInputEl('<div><input ng-model="result" uib-typeahead="state.name for state in states| filter:$viewValue" typeahead-show-hint="true"></div>');
+    });
+
+    it('should show hint when input matches first match', function() {
+      var hintEl = findInput(element);
+
+      expect(hintEl.val()).toEqual('');
+      changeInputValueTo(element, 'Alas');
+      expect(hintEl.val()).toEqual('Alaska');
+    });
+
+    it('should not show hint when input does not match first match', function() {
+      var hintEl = findInput(element);
+
+      expect(hintEl.val()).toEqual('');
+      changeInputValueTo(element, 'las');
+      expect(hintEl.val()).toEqual('');
+    });
+
+    it('should reset hint when a match is clicked', function() {
+      var hintEl = findInput(element);
+
+      expect(hintEl.val()).toEqual('');
+      changeInputValueTo(element, 'Alas');
+      expect(hintEl.val()).toEqual('Alaska');
+
+      var match = findMatches(element).find('a').eq(0);
+      match.click();
+      $scope.$digest();
+      expect(hintEl.val()).toEqual('');
+    });
+
+    it('should reset hint when click outside', function() {
+      var hintEl = findInput(element);
+
+      expect(hintEl.val()).toEqual('');
+      changeInputValueTo(element, 'Alas');
+      expect(hintEl.val()).toEqual('Alaska');
+
+      $document.find('body').click();
+      $scope.$digest();
+      expect(hintEl.val()).toEqual('');
+    });
+
+    it('should reset hint on enter', function() {
+      var hintEl = findInput(element);
+
+      expect(hintEl.val()).toEqual('');
+      changeInputValueTo(element, 'Alas');
+      expect(hintEl.val()).toEqual('Alaska');
+      triggerKeyDown(element, 13);
+      expect(hintEl.val()).toEqual('');
+    });
+
+    it('should reset hint on tab', function() {
+      var hintEl = findInput(element);
+
+      expect(hintEl.val()).toEqual('');
+      changeInputValueTo(element, 'Alas');
+      expect(hintEl.val()).toEqual('Alaska');
+      triggerKeyDown(element, 9);
+      expect(hintEl.val()).toEqual('');
+    });
+
+    it('should reset hint on escape key', function() {
+      var hintEl = findInput(element);
+
+      expect(hintEl.val()).toEqual('');
+      changeInputValueTo(element, 'Alas');
+      expect(hintEl.val()).toEqual('Alaska');
+      triggerKeyDown(element, 27);
+      expect(hintEl.val()).toEqual('');
+    });
+  });
 
   describe('append to element id', function() {
     it('append typeahead results to element', function() {

Diff for: src/typeahead/typeahead.js

@@ -71,6 +71,8 @@ angular.module('ui.bootstrap.typeahead', ['ui.bootstrap.position'])
     //binding to a variable that indicates if dropdown is open
     var isOpenSetter = $parse(attrs.typeaheadIsOpen).assign || angular.noop;
 
+    var showHint = originalScope.$eval(attrs.typeaheadShowHint) || false;
+
     //INTERNAL VARIABLES
 
     //model setter executed upon match selection
@@ -111,6 +113,33 @@ angular.module('ui.bootstrap.typeahead', ['ui.bootstrap.position'])
       'aria-owns': popupId
     });
 
+    //add read-only input to show hint
+    if (showHint) {
+      var inputsContainer = angular.element('<div></div>');
+      inputsContainer.css('position', 'relative');
+      element.after(inputsContainer);
+      var hintInputElem = element.clone();
+      hintInputElem.attr('placeholder', '');
+      hintInputElem.val('');
+      hintInputElem.css({
+        'position': 'absolute',
+        'top': '0px',
+        'left': '0px',
+        'border-color': 'transparent',
+        'box-shadow': 'none',
+        'opacity': 1,
+        'background': 'none 0% 0% / auto repeat scroll padding-box border-box rgb(255, 255, 255)',
+        'color': '#999'
+      });
+      element.css({
+        'position': 'relative',
+        'vertical-align': 'top',
+        'background-color': 'transparent'
+      });
+      inputsContainer.append(hintInputElem);
+      hintInputElem.after(element);
+    }
+
     //pop-up element used to display matches
     var popUpEl = angular.element('<div uib-typeahead-popup></div>');
     popUpEl.attr({
@@ -132,10 +161,17 @@ angular.module('ui.bootstrap.typeahead', ['ui.bootstrap.position'])
       popUpEl.attr('popup-template-url', attrs.typeaheadPopupTemplateUrl);
     }
 
+    var resetHint = function() {
+      if (showHint) {
+        hintInputElem.val('');
+      }
+    };
+
     var resetMatches = function() {
       scope.matches = [];
       scope.activeIdx = -1;
       element.attr('aria-expanded', false);
+      resetHint();
     };
 
     var getMatchId = function(index) {
@@ -196,6 +232,16 @@ angular.module('ui.bootstrap.typeahead', ['ui.bootstrap.position'])
             if (selectOnExact && scope.matches.length === 1 && inputIsExactMatch(inputValue, 0)) {
               scope.select(0);
             }
+
+            if (showHint) {
+              var firstLabel = scope.matches[0].label;
+              if (inputValue.length > 0 && firstLabel.slice(0, inputValue.length).toUpperCase() === inputValue.toUpperCase()) {
+                hintInputElem.val(inputValue + firstLabel.slice(inputValue.length));
+              }
+              else {
+                hintInputElem.val('');
+              }
+            }
           } else {
             resetMatches();
             isNoResultsSetter(originalScope, true);
@@ -377,6 +423,10 @@ angular.module('ui.bootstrap.typeahead', ['ui.bootstrap.position'])
       }
       // Prevent jQuery cache memory leak
       popUpEl.remove();
+
+      if (showHint) {
+          inputsContainer.remove();
+      }
     });
 
     var $popup = $compile(popUpEl)(scope);