Troubleshooting Problems with the Javascript Array Constructor

One question I have is why it's not recommended to declare an array like this:

 var arr = new Array()

I always thought that declaring with [] was safer in case of accidentally overwriting the Array object, but...

Array = 1;
var arr = [] // boom  
TypeError: Cannot read property 'slice' of undefined

Personally, I tend to use var arr = [], especially after encountering such issues. Now I'm curious about what exactly makes using [] better than Array other than potential speed advantages.

javascriptarraysconstructor

Answer №1

My initial assumption was that using square brackets [] would provide some level of protection against overwriting the Array object, but...

This is only true under EcmaScript 5 and not EcmaScript 3, meaning it may not work on older browsers.

You can find more information in the specification at

  1. When array is created using the expression new Array(), where Array is the standard built-in constructor with that name.

The highlighted text was an addition made in EcmaScript 5 and was not present in EcmaScript 3.

Answer №2

Both options serve the same purpose, with one exception:

These values are not the same:

var array = new Array(3);  // <-- Creates an array with length 3
var array = [3];

//If you wanted to use the `Array` to create an array with one element, use:
var array = new Array();
array[0] = 3;

[] is not only simpler but also more consistent. The Array constructor should only be used when creating arrays with a specific initial size.

Answer №3

There are already numerous similar posts on this topic.

Check out the following:

What is the best practice in JavaScript for using [] instead of new array?

Also, take a look at:

Understanding the use of JavaScript's new Array(n) Declaration

Answer №4

In my opinion, whether you use new Array() or =[] doesn't make much of a difference. Nowadays, most browsers' Javascript engines are intelligent enough to optimize small implementation discrepancies. Personally, I tend to opt for =[] simply to reduce the size of the javascript source by shaving off some extra bytes.

Answer №5

After conducting a trial, I discovered that overriding window.Array with anything other than a function causes it to malfunction.

Answer №6

In reality, there isn't any specific mention of this in JavaScript. Therefore, you must adhere to the conventions outlined in the standard for variable declarations.

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