Why `new Array()` and `Array()` behaves the same in Javascript?

Question

Here is the examples

Array(1,2,3)
> [1,2,3]
new Array(1,2,3)
> [1,2,3]
Array(3)
> [undefined, undefined, undefined]
new Array(3)
> [undefined, undefined, undefined]

I saw some comments about "never use Array with new". But I can't understand as I found Array and new Array seems to behave the same in Javascript.. Why do they behave the same? And why should one usage be preferred over the other?

I know [] literal syntax should usually be used instead of Array, I was just wondering what Array is..

Is it a constructor function? If it is a constructor function, why could it be used without new?

Actually neither new Array() nor Array() should be used. Use the literal syntax instead, i.e. [1, 2, 3]. Btw there is nothing in JavaScript from stopping you to call a constructor function without new. — helpermethod
– helpermethod, Commented Jun 1, 2015 at 12:07
care to share the comments you are mentioning so we know the context? :) I actually prefer the simple [] version :) — Icepickle
– Icepickle, Commented Jun 1, 2015 at 12:07
Don't use either Array(1,2,3) or new Array(1,2,3). Always use [1,2,3]. — TaoPR
– TaoPR, Commented Jun 1, 2015 at 12:09
@helpermethod I know [] is usually the best choice.. Just wondering what Array actually is.. — Hanfei Sun
– Hanfei Sun, Commented Jun 1, 2015 at 12:11
@Salketer Because new Array() behaves in unexpected ways. E.g. new Array(8) initializes an 8 element array, whereas new Array(8, 9) initializes an array with the elements 8 and 9. [8] on the other hand gives you an array containing the element 1. Also [] is shorter. — helpermethod
– helpermethod, Commented Jun 1, 2015 at 12:32

zerkms · Accepted Answer · 2015-06-01 12:13:02Z

8

When Array is called as a function rather than as a constructor, it creates and initialises a new Array object. Thus the function call Array(…) is equivalent to the object creation expression new Array(…) with the same arguments.

http://es5.github.io/#x15.4.1

answered Jun 1, 2015 at 12:13

zerkms

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1 Comment

AmmarCSE Over a year ago

Nice! looked all over documentation, but you found it! :)

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