.slice.call vs .push in javascript

Question

One of my friends uses [].slice.call() to fill an array with matched elements.

I wonder how this works. I just know the Array.prototype.push to fill an array.

Also I have seen there is a difference in both techniques to fill an array.

So my questions are:

How does Array.prototype.slice help to fill an array?
What are the roles of Array.prototype.slice and Array.prototype.push to make objects and arrays?

var arr=[];
var arr=[].slice.call($('[id^=name]'));
//arr.push($('[id^=name]'))
console.log(arr)

Pointy · Accepted Answer · 2014-02-15 14:49:41Z

The .slice() method of arrays returns a shallow copy of a portion of an array. It's written as a method on the Array prototype, so the array it operates on is the array in whose context it's invoked. Normally that'd be something like this:

var newArray = oldArray.slice(2, 4);

When you call the .slice() method with .call(), you can control the value of this explicitly. In your friend's code, he's passing a jQuery object as the this value. Because there are no other parameters, .slice() returns a shallow copy of the jQuery object in its entirety, as a new array. (Like some other similar methods, .slice() will work on anything that looks like an array: basically, anything that has a .length property and numerically-indexed properties of interest. A jQuery object fits that description.)

However, since jQuery already has a built-in method to return a plain array of all matched elements, your friend should not bother doing that anymore:

var plainArray = $('[id^=name]').get();

That does exactly the same thing. Using .slice() isn't wrong, but it's kind-of pointless.

Ha ha thanks - you must have been away because there are weeds and stuff growing on me here
Somebody should compile a book of Mr. Crowder's excellent deleted answers :)

sqykly · Accepted Answer · 2014-02-15 14:58:32Z

How about $('[id^=name]').get()?

The [].slice.call method leverages the array-like length and numeric key properties of jQuery objects to re-use the intentionally generic methods of Array.prototype. The method Array.prototype.slice is documented by the standard to return a new Array object by performing a specific algorithm that accesses numeric-keyed properties in sequence of the this object - regardless of its type - assigning the values to sequential elements of the new Array.

I wouldn't use either approach, because jQuery has get(), which is documented to return an array of the elements matched. Why use a more obscure or less direct approach?

Ash · Accepted Answer · 2014-02-15 14:59:54Z

1

I does't have any specified reason for this case, but The thing i know is, .slice() also used to create another instance of an array, And here the slice add a space to its instance because it have no parameters.

Javascript is the language where you perform a Single operations in 1000's of different ways ! its depend on your choice! But, We must have to follow the syntax that is made for particular operation.

answered Feb 15, 2014 at 14:59

Ash

1,42015 silver badges32 bronze badges

Collectives™ on Stack Overflow

.slice.call vs .push in javascript

3 Answers 3

2 Comments

1 Comment

Comments

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

2 Comments

1 Comment

Comments

Related