Using Object.create() in earlier versions of JavaScript

Question

I am trying to use pdf.js in an XFA PDF that only supports JavaScript 1.5 and therefore doesn't recognize Object.create() and call(). There are nearly 30 uses of Object.create() in pdf.js.

Is there a way I can add a function to extend Object() to include create()? It's just for the purpose of backwards compatibility.

Kyle

"...therefore doesn't recognize Object.create() and call()..." Pretty sure call has been in JavaScript since about 1998. — T.J. Crowder
– T.J. Crowder, Commented Aug 22, 2014 at 15:31
You just have to look at the MDN documentation for a polyfill: developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/… — Felix Kling
– Felix Kling, Commented Aug 22, 2014 at 15:34
(That's so meta -- to use Adobe Reader to parse PDFs using PDF.js) — async5
– async5, Commented Aug 22, 2014 at 15:45
Yes I know. But using the Acrobat JS API for what I was doing was crashing Adobe Reader 10. — dcidev
– dcidev, Commented Aug 22, 2014 at 15:49
possible duplicate of Javascript Object.create not working in Firefox — cookie monster
– cookie monster, Commented Aug 22, 2014 at 15:54

dcidev · Accepted Answer · 2014-08-22 15:59:36Z

0

Got it:

if(typeof Object.create !== "function") {
    Object.create = function (o) {
        function F() {}
        F.prototype = o;
        return new F();
    };
}

Thanks for your responses. Ya, I don't know why I included call() in there.

Kyle

edited Aug 22, 2014 at 15:59

answered Aug 22, 2014 at 15:46

dcidev

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5 Comments

T.J. Crowder Over a year ago

Note that the real Object.create has a second argument, which cannot be shimmed on pre-ES5 environments. When shimming, I recommend looking to see if you've gotten a second argument and throwing an exception.

cookie monster Over a year ago

In addition to what @T.J.Crowder said, the standard Object.create lets you set null as the prototype, but the typical shim that you've posted will fail when creating the new object. So you may want to test for null, and substitute Object.prototype in its place.

cookie monster Over a year ago

...and actually, since this seems to be for Mozilla's JS, you could probably use __proto__ as the patch, which will accept null if I recall. var new_o = {}; new_o.__proto__ = o; return new_o;

dcidev Over a year ago

Good catch cookie. I will use that.

dcidev Over a year ago

T.J. luckily for me pdf.js doesn't use the second argument for Object.create.

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