What is array literal notation in javascript and when should you use it?

JavascriptArraysJslintLiterals

Javascript Problem Overview


JSLint is giving me this error:

>Problem at line 11 character 33: Use the array literal notation [].

var myArray = new Array();

What is array literal notation and why does it want me to use it instead?

It shows http://www.w3schools.com/JS/js_obj_array.asp">here</a> that new Array(); should work fine... is there something I'm missing?

Javascript Solutions


Solution 1 - Javascript

array literal notation is where you define a new array using just empty brackets. In your example:

var myArray = [];

It is the "new" way of defining arrays, and I suppose it is shorter/cleaner.

The examples below explain the difference between them:

var a = [],            // these are the same
    b = new Array(),   // a and b are arrays with length 0

    c = ['foo', 'bar'],           // these are the same
    d = new Array('foo', 'bar'),  // c and d are arrays with 2 strings

    // these are different:
    e = [3],             // e.length == 1, e[0] == 3
    f = new Array(3);   // f.length == 3, f[0] == undefined

>Reference: https://stackoverflow.com/a/931875/177125">What’s the difference between “Array()” and “[]” while declaring a JavaScript array?

Solution 2 - Javascript

See also: What’s wrong with var x = new Array();

Aside from the Crockford argument, I believe it is also due to the fact that other languages have similar data structures that happen to use the same syntax; for example, Python has lists and dictionaries; see the following examples:

// this is a Python list
a = [66.25, 333, 333, 1, 1234.5]

// this is a Python dictionary
tel = {'jack': 4098, 'sape': 4139}

Isn't it neat how Python is also grammatically correct Javascript? (yes, the ending semi-colons are missing, but those aren't required for Javascript, either)

Thus, by reusing common paradigms in programming, we save everyone from having to relearn something that shouldn't have to.

Solution 3 - Javascript

Aside from the Crockford argument, jsPerf says that it's faster. http://jsperf.com/new-vs-literal-array-declaration

Solution 4 - Javascript

After looking at @ecMode jsperf, I did some further tests.

When using push to add to the array new Array() is considerably faster on Chrome:

http://jsperf.com/new-vs-literal-array-declaration/2

Using index to add is slightly faster for [].

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