Why does jQuery Extend Deep Copy not recursively copy an object?

问题

I've searched everywhere and found similar questions with answers that didn't really address my issue so I apologize if this seems like a repeat, but it appears from my experimenting that jQuery's deep copy function doesn't actually work as it's described (or maybe I'm misreading its description).

Here's an example demonstrating the problem I'm having: http://jsfiddle.net/wcYsH/

Or this for download: https://github.com/kevroy314/jQuery-Extend-Test

Why does the data in the previous copy get changed when the deep copy is manipulated?

回答1:

For one, you aren't creating normal objects.

I'm looking at the source code for jQuery 1.7.2 for extend.

https://github.com/jquery/jquery/blob/master/src/core.js

And I'm noticing the line:

if ( deep && copy && ( jQuery.isPlainObject(copy) || (copyIsArray = jQuery.isArray(copy))

has to evaluate to true to do deep copying. copy is just part of the current object being copied.

But you aren't creating "plain" objects. You are creating objects generated by invoking a constructor with the new operator.

Now, in isPlainObject, it seems these lines have to be evaluated. (where hasOwn is hasOwn = Object.prototype.hasOwnProperty

    try {
        // Not own constructor property must be Object
        if ( obj.constructor &&
            !hasOwn.call(obj, "constructor") &&
            !hasOwn.call(obj.constructor.prototype, "isPrototypeOf") ) {
            return false;
        }
    } catch ( e ) {
        // IE8,9 Will throw exceptions on certain host objects #9897
        return false;
    }

And there's where it concludes it's not a "plainObject".

This makes sense when you consider objects with a constructor probably ought to be created via that constructor or at least use some sort of "clone" method as you'd see in other languages/frameworks.

来源：https://stackoverflow.com/questions/10505144/why-does-jquery-extend-deep-copy-not-recursively-copy-an-object