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What is the most efficient way to clone a JavaScript object?
I need to copy an (ordered, not associative) array of objects. I'm using jQuery. I initially tried
jquery.extend({}, myArray)
but, naturally, this gives me back an object, where I need an array (really love jquery.extend, by the way).
So, what's the best way to copy an array?
Since Array.slice() does not do deep copying, it is not suitable for multidimensional arrays:
var a =[[1], [2], [3]];
var b = a.slice();
b.shift().shift();
// a is now [[], [2], [3]]
Note that although I've used shift().shift() above, the point is just that b[0][0] contains a pointer to a[0][0] rather than a value.
Likewise delete(b[0][0]) also causes a[0][0] to be deleted and b[0][0]=99 also changes the value of a[0][0] to 99.
jQuery's extend method does perform a deep copy when a true value is passed as the initial argument:
var a =[[1], [2], [3]];
var b = $.extend(true, [], a);
b.shift().shift();
// a is still [[1], [2], [3]]
$.extend(true, [], [['a', ['c']], 'b'])
That should do it for you.
I realize you're looking for a "deep" copy of an array, but if you just have a single level array you can use this:
Copying a native JS Array is easy. Use the Array.slice() method which creates a copy of part/all of the array.
var foo = ['a','b','c','d','e'];
var bar = foo.slice();
now foo and bar are 5 member arrays of 'a','b','c','d','e'
of course bar is a copy, not a reference... so if you did this next...
bar.push('f');
alert('foo:' + foo.join(', '));
alert('bar:' + bar.join(', '));
you would now get:
foo:a, b, c, d, e
bar:a, b, c, d, e, f
Everything in JavaScript is pass by reference, so if you want a true deep copy of the objects in the array, the best method I can think of is to serialize the entire array to JSON and then de-serialize it back.
If you want to use pure JavaScript then try this:
var arr=["apple","ball","cat","dog"];
var narr=[];
for(var i=0;i<arr.length;i++){
narr.push(arr[i]);
}
alert(narr); //output: apple,ball,vat,dog
narr.push("elephant");
alert(arr); // output: apple,ball,vat,dog
alert(narr); // apple,ball,vat,dog,elephant
how about complex types? when array contains objects... or any else
My variant:
Object.prototype.copy = function(){
var v_newObj = {};
for(v_i in this)
v_newObj[v_i] = (typeof this[v_i]).contains(/^(array|object)$/) ? this[v_i].copy() : this[v_i];
return v_newObj;
}
Array.prototype.copy = function(){
var v_newArr = [];
this.each(function(v_i){
v_newArr.push((typeof v_i).contains(/^(array|object)$/) ? v_i.copy() : v_i);
});
return v_newArr;
}
It's not final version, just an idea.
PS: method each and contains are prototypes also.
I've come across this "deep object copy" function that I've found handy for duplicating objects by value. It doesn't use jQuery, but it certainly is deep.
http://www.overset.com/2007/07/11/javascript-recursive-object-copy-deep-object-copy-pass-by-value/
I plan on releasing this code in the next version of jPaq, but until then, you can use this if your goal is to do a deep copy of arrays:
Array.prototype.clone = function(doDeepCopy) {
if(doDeepCopy) {
var encountered = [{
a : this,
b : []
}];
var item,
levels = [{a:this, b:encountered[0].b, i:0}],
level = 0,
i = 0,
len = this.length;
while(i < len) {
item = levels[level].a[i];
if(Object.prototype.toString.call(item) === "[object Array]") {
for(var j = encountered.length - 1; j >= 0; j--) {
if(encountered[j].a === item) {
levels[level].b.push(encountered[j].b);
break;
}
}
if(j < 0) {
encountered.push(j = {
a : item,
b : []
});
levels[level].b.push(j.b);
levels[level].i = i + 1;
levels[++level] = {a:item, b:j.b, i:0};
i = -1;
len = item.length;
}
}
else {
levels[level].b.push(item);
}
if(++i == len && level > 0) {
levels.pop();
i = levels[--level].i;
len = levels[level].a.length;
}
}
return encountered[0].b;
}
else {
return this.slice(0);
}
};
The following is an example of how to call this function to do a deep copy of a recursive array:
// Create a recursive array to prove that the cloning function can handle it.
var arrOriginal = [1,2,3];
arrOriginal.push(arrOriginal);
// Make a shallow copy of the recursive array.
var arrShallowCopy = arrOriginal.clone();
// Prove that the shallow copy isn't the same as a deep copy by showing that
// arrShallowCopy contains arrOriginal.
alert("It is " + (arrShallowCopy[3] === arrOriginal)
+ " that arrShallowCopy contains arrOriginal.");
// Make a deep copy of the recursive array.
var arrDeepCopy = arrOriginal.clone(true);
// Prove that the deep copy really works by showing that the original array is
// not the fourth item in arrDeepCopy but that this new array is.
alert("It is "
+ (arrDeepCopy[3] !== arrOriginal && arrDeepCopy === arrDeepCopy[3])
+ " that arrDeepCopy contains itself and not arrOriginal.");
You can play around with this code here at JS Bin.
[]instead of{}