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Editorial Team
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Asked: 2026-05-15T03:32:31+00:00

When I try to call Test function I get an error. How to fix

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When I try to call “Test” function I get an error.
How to fix that? (no jquery!)

Browser:firefox
error:

TypeError: this.Test is not a function

    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
        <title>Untitled Document</title>
        <script type="text/javascript">



            MyClass = function(){
            }

            MyClass.prototype = {

                Init: function(){
                    var txt = document.getElementById("text");

                    if (txt.addEventListener) {
                        txt.addEventListener("keyup", this.Foo, true)
                    }


                },

                Foo: function(){
                    this.Test();
                },

                Test: function(){
                    alert('OK');
                }


            }
            window.onload = function(){
                obj = new MyClass;
                obj.Init();
            }
        </script>
    </head>
    <body>
    <textarea id="text" rows="10">
    </textarea>
    </div>
</body>
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1 Answer

  1. Editorial Team

    It’s because you reference this.Foo as the event, what actually happens is that it copies that function out of the object scope, ergo this does not exist. What most people do is use an anonymous function / wrapper around the event.

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