Defining custom objects and functions in JavaScript

Question

Can someone explain what is wrong with this JavaScript example, and how to fix it if possible?

    // I can define objects / functions like this.
    window['Custom'] = function() { };
    //Works...I now have a 'Custom' function in scope... I can now do this...

    var c = new Custom(); // WORKS!!

    //This does not seem to work!
    window['Custom.prototype.msg'] = function(msg) {
        alert(msg);
    };

    // I DO NOT WANT TO DO THIS!
    Custom.prototype.msg = function(msg) { alert(msg); };


    x.msg("Hello");
    //FireFox Error: TypeError: x.msg is not a function...
    // HOW DO I FIX THIS!?

Pointy · Accepted Answer · 2012-08-30 13:37:26Z

1

You want:

window.Custom.prototype.msg = function(msg) { ... }

The bracket notation takes a string, but the string won't be interpreted as an object graph expression; it's just a string. Thus, window["Custom.prototype.msg"] creates a global function called "Custom.prototype.msg".

edit — this would also work:

window["Custom"]["prototype"]["msg"] = function(msg) { ... }

So if you're working with those dotted list expressions for some reason, if you want them to be interpreted as such you'll have to break them up yourself.

answered Aug 30, 2012 at 13:37

Pointy

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8 Comments

Matthew Layton Over a year ago

That's exactly what I don't want, sorry see my revised example.

Pointy Over a year ago

@activwerx well want or don't want whatever, your code won't work as written because it's simply not what JavaScript does. I'll add another suggestion to the answer.

Matthew Layton Over a year ago

Thanks, sorry for the confusion!

MalSu Over a year ago

As a curiosity, is there any reason in particular why you wouldn't want to use that notation?

Matthew Layton Over a year ago

And thanks for the update, I will accept your answer on that basis!

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