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Calling A Prototype Function Via Button Click Not Working

- 1 answer

This is part of a program that was built in attempt to use the Model-View-Controller design pattern. As I understand it, I cannot use the this keyword itself in the function handling a click event. But when I use _this instead, I got the error : Uncaught TypeError: _this.saveCastle is not a function.

Also, when I used console.log on _this, it returned the global object and I had believed it should point to the local function.

Any feedback is appreciated, thanks.

var CreateCastleView = (function () {

      function CreateCastleView(document, controller, model, validationResult) {
        this.document = document;
        this.controller = controller;
        this.model = model;
        this.validationResult = validationResult;

        var _this = this;

        this.document.getElementById('save').addEventListener('click', function() {
            return _this.saveCastle();
        });

      CreateCastleView.prototype.saveCastle = function() {
          console.log("This isn't being called");
      };
      return CreateCastleView;
})();
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Answer

I can't be 100% sure because you aren't showing your client code of the object, however the following produces the desired results:

  1 <html>
  2   <head>
  3     <script>
  4 document.addEventListener( "DOMContentLoaded", function( event ){
  5   var CreateCastleView = (function () {
  6 
  7         function CreateCastleView(document, controller, model, validationResult) {
  8           this.document = document;
  9           this.controller = controller;
 10           this.model = model;
 11           this.validationResult = validationResult;
 12 
 13           var _this = this;
 14 
 15           this.document.getElementById('save').addEventListener('click', function() {
 16               return _this.saveCastle();
 17           });
 18         }
 19 
 20         CreateCastleView.prototype.saveCastle = function() {
 21             console.log("This isn't being called");
 22         };
 23         return CreateCastleView;
 24   })();
 25 new CreateCastleView( document );
 26 });
 27     </script>
 28   </head>
 29   <body>
 30     <h1 id='save'>Click me</h1>
 31   </body>
 32 </html>

The two key pieces being on line #25 and #18. If you invoke the CreateCastleView as a function (omitting the 'new' keyword) then the result is your described problem. Without invoking the function as a constructor or method the default 'this' object is used, which is usually aliasing the window global.

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source: stackoverflow.com
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