Duplicate object in javascript

Question

I see two ways to duplicate objects

1.

var a={c:1}
var b=a;
alert(b.c);//alert 1

2.

var a={c:2};
var b={};
for (i in a)
{b[i]=a[i];} 
alert(b.c);//alert 1

The first are shorter than the second so what is the efficiency in the second example?

Answer 1

In the first version you don't duplicate/clone the object you simply make a extra reference to it:

var a = { a: 1 };
var b = a;
b.a = 2;

console.log(a.a); // 2;

To clone an object there is numbers of libraries that can do that for you:

var b = $.extend({}, a); // Make a shallow clone (jQuery)
var b _.extend({}, a); // Make a shallow clone (underscore.js)

var b = $.extend(true, {}, a); // Make a deep clone (jQuery);

Or you can do it natively:
Simple clone:

var b = {};
var prop;

for (prop in a) {
    b[prop] = a[prop];
}

---

Scratch of a deep clone function:

function deepClone(obj) {
    var r;
    var i = 0,
    var len = obj.length;
    // string, number, boolean
    if (typeof obj !== "object") { 
        r = obj;
    }
    // Simple check for array
    else if ( len ) { 
        r = [];
        for ( ; i < len; i++ ) {
            r.push( deepClone(obj[i]) );
        }
    } 
    // Simple check for date
    else if ( obj.getTime ) { 
        r = new Date( +obj );
    }
    // Simple check for DOM node
    else if ( obj.nodeName ) { 
        r = obj;
    }
    // Object
    else { 
        r = {};
        for (i in obj) {
            r[i] = deepClone(obj[i]);
        }
    }

    return r;
}