Create an array with or without `new`

Question

There are two ways to create an array using the array constructor

new Array(1,2,3)
Array(1,2,3)

I would say that the first (with the new keyword) is preferred or is it of no importance ?

UPDATE: In my case I use this type of array construction because I do:

new Array(someNum).join('x');

True, I've updated my post to show an example of why I'm using this, thnx! — Jeanluca Scaljeri
– Jeanluca Scaljeri, Commented Aug 18, 2015 at 14:39

thefourtheye · Accepted Answer · 2015-08-18 13:36:04Z

4

If a function is meant to be used only as a constructor function, then one can use the common pattern,

function ConstructorFunction() {
    // If the current object is not an instance of `ConstructorFunction`
    if (!(this instanceof ConstructorFunction)) {
        return new ConstructorFunction();
    }
    ...
}

Something similar to that would be done in the Array constructor as well.

Note: It is always better to use new, if you intend to use a function as a constructor function.

answered Aug 18, 2015 at 13:36

thefourtheye

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1 Comment

RobG Over a year ago

"Something similar to that would be done in the Array constructor as well". Not according to ECMA-262: "When Array is called as a function rather than as a constructor, it also creates and initializes a new Array object", so it doesn't test its this, it always creates a new instance.

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