Why return is required while defining my module using requirejs?

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Hi,

Following is my code:

HTML:

HTML

<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <title>Using Require js for modular loading of scripts.</title>
    <!--Requirejs first loads the module that is specified in data-main .. So it will load the module init,init has two dependencies first is knockout so it loads the knockout first, then myAppViewModel next -->
    <script type="text/javascript" data-main="scripts/init.js" src="scripts/require.js"></script>
</head>
<body>
    Name : <span data-bind="text: myName"></span>
</body>
</html>

init.js:

JavaScript

require(['knockout-3.2.0', 'myAppViewModel'], function(ko, myAppViewModel) {
    ko.applyBindings(new myAppViewModel());
});

myAppViewModel.js

JavaScript

define(function () {
    return function myAppViewModel() {
        this.myName = 'Sudheer';
    };
});

If i remove return from above code. It says myAppViewModel() is not a constructor. Why return is required in this context?

Posted 8-Dec-14 19:24pm

Sudheer Reddy K

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Kornfeld Eliyahu Peter · Accepted Answer · 2014-12-08T19:52:00

It is beginning with new myAppViewModel part...new in JavaScript is looks like a keyword but actually an operator!!! As any operator also new has to return a value!
What actually new does is calling the function you gave him as parameter - and yes, this is a function even you like to think it as a class (in fact in JavaScript there is no difference more than semantics)...
In the normal JavaScript environment you would create myAppViewModel without the envelop that knockout.js requires, like this:

JavaScript

function myAppViewModel() {
  this.myName = 'Sudheer';
}

In this case new operator was able to create a new class out of the function without return too, but in knockout.js you enclose your function/class inside an other function/class (define it called) you have to explicitly return the correct answer to new...
That's the reason it will not work without return at the beginning...