Working with objects and creating methods in JavaScript that return values

Question

This has been driving me crazy because I can't find anything on Google. Maybe it's because I don't know the right terminology to search right. But this is what I'm trying to do.

I want to create a function that acts like an object. I'm think it's called a method, though I could be wrong.

Check this out, this is some pseudocode of what I would like it to do.

function myMethod(){
var p = this.getAttribute('x');
var p = p+1;
return p;
}

function otherFunction(){
var q = document.getElementByID('Element').myMethod();
alert(q);
}

So, I can't get this to work. It keeps saying myMethod() is undefined and not a function.

are you trying to call myMethod on the 'Element' that is found using the document.getElementById()? — bittersweetryan
– bittersweetryan, Commented Sep 16, 2011 at 20:34

pimvdb · Accepted Answer · 2011-09-16 20:56:11Z

4

If you want myMethod to be available on elements, you'd have to append it to elements' prototype.

Element.prototype.myMethod = myMethod;

The concept of prototype is big, but it comes down to the fact that instances of functions have a function available in the way that you describe as 'like an object'.

In this case, any element on the page is an instance of the Element function. Therefore, any element will have .myMethod available, which you can call. (Element is a function although you don't really deal with that - the instances are available because you put them there in HTML, so you bypass using Element.)

Second, if you have var p, then another var p does not make much sense. Just use p = p + 1, or p++ (shortcut for adding one).

edited Sep 16, 2011 at 20:56

answered Sep 16, 2011 at 20:34

pimvdb

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1 Comment

Chase Over a year ago

The Element and HTMLElement interfaces (and the rest & their prototypes) aren't exposed in IE7 and below, might be something to watch out for.

jondavidjohn · Accepted Answer · 2011-09-16 20:33:56Z

function myMethod(element){
    var p = element.getAttribute('x');
    var p = p+1;
    return p;
}

function otherFunction(){
    var q = myMethod(document.getElementByID('Element'));
    alert(q);
}

Obviously, it would be better to not declare these in the global scope, but basically is that javascript is looking for a myMethod() that is a member of the DOM Element you are selecting, but you have actually declared the function standing alone.

Another option would be to add the method via prototype inheritance.

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