title: Angularjs ngDisabled comparison expression not evaluating correctly
body: <p>I am attempting to have a button be enabled or disabled in an angularjs app based on whether a comparison of two text fields evaluates to true or false. I have provided example code below and also made it available in a plunker here <a href="http://plnkr.co/edit/rzly8hy21048YGzsx2gW?p=preview" rel="noreferrer">http://plnkr.co/edit/rzly8hy21048YGzsx2gW?p=preview</a></p>
  
  <p>As you can see when you input a string to match the stored string the expression evaluates correctly however the button never becomes available.</p>
  
  <p>Any help would be appreciated.</p>
  
  <p>Here is the HTML</p>
  
  <pre><code>    &lt;!DOCTYPE html&gt;
  &lt;html ng-app="plunker"&gt;
  
    &lt;head&gt;
      &lt;meta charset="utf-8" /&gt;
      &lt;title&gt;AngularJS Plunker&lt;/title&gt;
      &lt;script&gt;document.write('&lt;base href="' + document.location + '" /&gt;');&lt;/script&gt;
      &lt;link rel="stylesheet" href="style.css" /&gt;
      &lt;script data-require="angular.js@1.2.x" src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.16/angular.min.js" data-semver="1.2.16"&gt;&lt;/script&gt;
      &lt;script src="app.js"&gt;&lt;/script&gt;
    &lt;/head&gt;
  
    &lt;body ng-controller="MainCtrl"&gt;
      &lt;button ng-click="updateCounter()"&gt;Increment count&lt;/button&gt;
      &lt;input type="text" ng-model="inputfield"&gt;
      &lt;input type="button" value="Continue" ng-disabled="{{inputfield !== startertext}}"&gt;
      &lt;br&gt;startertext: {{startertext}}
      &lt;br&gt;nputfield: {{inputfield}}
      &lt;br&gt;test: {{inputfield !== startertext}}
  
    &lt;/body&gt;
  
  
  &lt;/html&gt;
  </code></pre>
  
  <p>And the Javascript file is below.</p>
  
  <pre><code>var app = angular.module('plunker', []);
  
  app.controller('MainCtrl', function($scope) {
    $scope.startertext = 'hello world';
  });
  </code></pre>