How do you check if a variable is an array in JavaScript? [duplicate]

Answer 1

For those who code-golf, an unreliable test with fewest characters:

function isArray(a) {
  return a.map;
}

This is commonly used when traversing/flattening a hierarchy:

function golf(a) {
  return a.map?[].concat.apply([],a.map(golf)):a;
}

input: [1,2,[3,4,[5],6],[7,[8,[9]]]]
output: [1, 2, 3, 4, 5, 6, 7, 8, 9]

Answer 2

When I posted this question the version of JQuery that I was using didn't include an isArray function. If it had have I would have probably just used it trusting that implementation to be the best browser independant way to perform this particular type check.

Since JQuery now does offer this function, I would always use it...

$.isArray(obj);

(as of version 1.6.2) It is still implemented using comparisons on strings in the form

toString.call(obj) === "[object Array]"

Answer 3

I noticed someone mentioned jQuery, but I didn't know there was an isArray() function. It turns out it was added in version 1.3.

jQuery implements it as Peter suggests:

isArray: function( obj ) {
    return toString.call(obj) === "[object Array]";
},

Having put a lot of faith in jQuery already (especially their techniques for cross-browser compatibility) I will either upgrade to version 1.3 and use their function (providing that upgrading doesn’t cause too many problems) or use this suggested method directly in my code.

Many thanks for the suggestions.

Answer 4

This is an old question but having the same problem i found a very elegant solution that i want to share.

Adding a prototype to Array makes it very simple

Array.prototype.isArray = true;

Now once if you have an object you want to test to see if its an array all you need is to check for the new property

var box = doSomething();

if (box.isArray) {
    // do something
}

isArray is only available if its an array

Answer 5

Something I just came up with:

if (item.length) //This is an array else //not an array

Answer 6

code referred from https://github.com/miksago/Evan.js/blob/master/src/evan.js

  var isArray = Array.isArray || function(obj) {
    return !!(obj && obj.concat && obj.unshift && !obj.callee);};