How does Prototype extend Objects?

Question

I've been reading up on the Prototype source code while learning Javascript. I've been wondering where is the code that is being used to extend Native Objects.

I've been seeing,

Object.extend(Function.prototype, (function() {
Object.extend(String.prototype, (function() {
Object.extend(Number.prototype, (function() {

all over the place and I can't find where the .extend function is coming from.

I've seen this:

  function extend(destination, source) {
    for (var property in source)
      destination[property] = source[property];
    return destination;
  }

at line 194-198 and wonder if this is the one. I can't find out how it is, if it is.

anyway, my question as I stated above is how/where does Prototype extend the Native objects.

Nick Craver · Accepted Answer · 2010-12-13 18:23:47Z

3

Yes, it is the function you're seeing, later in the code you'll see it used to get Object.extend, like this:

extend(Object, {
    extend: extend, //here's where the magic gets added
    inspect: inspect,
    toJSON: NATIVE_JSON_STRINGIFY_SUPPORT ? stringify : toJSON,
    toQueryString: toQueryString,
    toHTML: toHTML,
    keys: Object.keys || keys,
    values: values,
    clone: clone,
    isElement: isElement,
    isArray: isArray,
    isHash: isHash,
    isFunction: isFunction,
    isString: isString,
    isNumber: isNumber,
    isDate: isDate,
    isUndefined: isUndefined
});

So it's calling extend() with itself as a property to add to theObject prototype, adding itself as the .extend method on Object.

answered Dec 13, 2010 at 18:23

Nick Craver

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3 Comments

Teej Over a year ago

I think I get what you mean here: keys:Object.keys. So Object.keys are actually the Object properties. What does the other '|| keys' do here?

Nick Craver Over a year ago

@Thorpe - It's saying if it already has Object.keys (a native browser version), use that, if not then use the keys function defined in that file: github.com/sstephenson/prototype/blob/master/src/prototype/lang/…

Teej Over a year ago

I thought so :) I believe that your answer was the best at explaining things. +1

Jacob Relkin · Accepted Answer · 2010-12-13 18:26:47Z

1

If you look at the source code here:
https://github.com/sstephenson/prototype/blob/master/src/prototype/lang/object.js you will see this:

alt text

edited Dec 13, 2010 at 18:26

answered Dec 13, 2010 at 18:21

Jacob Relkin

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2 Comments

Teej Over a year ago

Hmm... where do I find this line?

Nick Craver Over a year ago

@Thorpe - github.com/sstephenson/prototype/blob/master/src/prototype/lang/…

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