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up vote 6 down vote favorite

what is the difference (if there is any) between

x = Array()

and

x = new Array()

in CoffeeScript (or JavaScript for that purpose)? Which one should I use?

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You might find this interesting: stackoverflow.com/questions/383402/… –  nickd Nov 20 '11 at 23:38

3 Answers 3

up vote 4 down vote accepted

The spec says:

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.

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up vote 5 down vote

I believe that both are equivalent. However, in JavaScript at least, you should always use the literal syntax:

x = []

But based on some tests in the browsers I have, Array(1, 2, 3) gives the same result as new Array(1, 2, 3), and same with Array(15) and new Array(15). Or just plain new Array().

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Correct, there are the exact same. –  Raynos Nov 20 '11 at 23:35
    
You should probably use x = [ ] in both JavaScript and CoffeeScript unless you need to pre-size the array for some reason. –  mu is too short Nov 20 '11 at 23:39
    
mu is exactly right: Use arr = new Array(n) (where n is a number) if and only if you're doing something performance-intensive where you know how large the array will be in advance, so the required memory is allocated all at once (in principle). –  Trevor Burnham Nov 21 '11 at 0:33
    
@minitech - why the "should"? –  RobG Nov 21 '11 at 0:52
    
@TrevorBurnham - there is no reason to believe that setting the length property will cause any memory to be allocated or improve performance. –  RobG Nov 21 '11 at 0:52
up vote 6 down vote

You should use the literal []. Reasons are outlined here. Using the Array() constructor can be ambiguous, since it accepts either a length or a list of elements:

new Array(5)   // []
new Array('5') // ['5']

[5]   // [5]
['5'] // ['5']

The reason you can use Array without the new operator is that internally it does a common trick with constructors:

function Thing(){
    if (!(this instanceof Thing)){
        return new Thing()
    }
    // ... define object
}

That is, if you call Thing() it will call new Thing() for you.

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