Uncaught TypeError when adding enumerable function to Object prototype

Question

I get a few type errors whenever I add an enumerable function to the prototype of Object.

jquery-1.10.2.js:2451 Uncaught TypeError: matchExpr[type].exec is not a function
    at tokenize (jquery-1.10.2.js:2451)
    at Function.Sizzle [as find] (jquery-1.10.2.js:1269)
    at init.find (jquery-1.10.2.js:5744)
    at change-project-controller.js:4
    at change-project-controller.js:255
tokenize @ jquery-1.10.2.js:2451
Sizzle @ jquery-1.10.2.js:1269
find @ jquery-1.10.2.js:5744
(anonymous) @ change-project-controller.js:4
(anonymous) @ change-project-controller.js:255

jquery-1.10.2.js:2451 Uncaught TypeError: matchExpr[type].exec is not a function
    at tokenize (jquery-1.10.2.js:2451)
    at Function.Sizzle [as find] (jquery-1.10.2.js:1269)
    at init.find (jquery-1.10.2.js:5744)
    at filter-by-registrant-controller.js:10
    at filter-by-registrant-controller.js:179
tokenize @ jquery-1.10.2.js:2451
Sizzle @ jquery-1.10.2.js:1269
find @ jquery-1.10.2.js:5744
(anonymous) @ filter-by-registrant-controller.js:10
(anonymous) @ filter-by-registrant-controller.js:179

jquery-1.10.2.js:2451 Uncaught TypeError: matchExpr[type].exec is not a function
    at tokenize (jquery-1.10.2.js:2451)
    at Function.Sizzle [as find] (jquery-1.10.2.js:1269)
    at init.find (jquery-1.10.2.js:5744)
    at registrations-controller.js:6
    at registrations-controller.js:412
tokenize @ jquery-1.10.2.js:2451
Sizzle @ jquery-1.10.2.js:1269
find @ jquery-1.10.2.js:5744
(anonymous) @ registrations-controller.js:6
(anonymous) @ registrations-controller.js:412

Index:290 Uncaught TypeError: Cannot read property 'registerFilter' of undefined
    at Index:290
(anonymous) @ Index:290

Notice that the last of the four errors does not have anything to do with jQuery.

This is the code that causes the error to occur:

Object.defineProperty(Object.prototype, "select", {

    enumerable: true,
    value: function () {

        return "hello world";

    }

});

I do not get the errors if I add the function as non-enumerable, like this:

Object.defineProperty(Object.prototype, "select", {

    enumerable: false,
    value: function () {

        return "hello world";

    }

});

Notice that the only difference is the enumerable member is set to false . Also if I change the enumerable function to be added to Array rather than Object the code runs fine.

The project I'm working on is not mine so I cannot share it and I have not been successful at reproducing the error on jsfiddle or in a simple HTML file.

Answer 1

I get a few type errors whenever I add an enumerable function to the prototype of Object.

Don't do that. As you've found, doing that will break a lot of unsuspecting code. The default state of things is that a blank object has no enumerable properties. Eg:

 var o = {}; for (var name in o) { console.log("This line never runs in a reasonable world."); } console.log("End"); 

By adding an enumerable property to Object.prototype , you break that:

 Object.prototype.foo = function() { }; var o = {}; for (var name in o) { console.log("I wasn't expecting to find: " + name); } console.log("End"); 

Adding things to Object.prototype is almost never a good idea. Adding enumerable things to it is always a Bad Idea™. All modern browsers support defineProperty , so if you must augment Object.prototype , do so with non-enumerable properties. (Note, though, that it's easy to introduce incompatibilities even with non-enumerable Object.prototype properties.) If you need to support obsolete browsers that don't support it, you need to leave Object.prototype alone.