How to check if an object is an array?

Question

I\'m trying to write a function that either accepts a list of strings, or a single string. If it\'s a string, then I want to convert it to an array with just the one item so

Answer 1

easiest and fastest way to check if an Object is an Array or not.

 var arr = [];
  arr.constructor.name ==='Array'  //return true;

or

arr.constructor ===Array //return true;

or you can make a utility function:

function isArray(obj){ return obj && obj.constructor ===Array}

usage:

isArray(arr); //return true

Answer 2

In your case you may use concat method of Array which can accept single objects as well as array (and even combined):

function myFunc(stringOrArray)
{
  var arr = [].concat(stringOrArray);

  console.log(arr);

  arr.forEach(function(item, i)
  {
    console.log(i, "=", item);
  })
}

myFunc("one string");

myFunc(["one string", "second", "third"]);

concat seems to be one of the oldest methods of Array (even IE 5.5 knows it well).

Answer 3

The best solution I've seen is a cross-browser replacement for typeof. Check Angus Croll's solution here.

The TL;DR version is below, but the article is a great discussion of the issue so you should read it if you have time.

Object.toType = function(obj) {
    return ({}).toString.call(obj).match(/\s([a-z|A-Z]+)/)[1].toLowerCase();
}
// ... and usage:
Object.toType([1,2,3]); //"array" (all browsers)

// or to test...
var shouldBeAnArray = [1,2,3];
if(Object.toType(shouldBeAnArray) === 'array'){/* do stuff */};

Answer 4

This is the fastest among all methods (all browsers supported):

function isArray(obj){
    return !!obj && obj.constructor === Array;
}

Answer 5

There is a nice example in Stoyan Stefanov's book JavaScript Patterns which suppose to handle all possible problems as well as utilize ECMAScript 5 method Array.isArray().

So here it is:

if (typeof Array.isArray === "undefined") {
    Array.isArray = function (arg) {
        return Object.prototype.toString.call(arg) === "[object Array]";
    };
}

By the way, if you are using jQuery, you can use it's method $.isArray()

Answer 6

If the only two kinds of values that could be passed to this function are a string or an array of strings, keep it simple and use a typeof check for the string possibility:

function someFunc(arg) {
    var arr = (typeof arg == "string") ? [arg] : arg;
}