How to check if an object is an array?

Posted By: Anonymous

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 I can loop over it without fear of an error.

So how do I check if the variable is an array?

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I’ve rounded up the various solutions below and created a jsperf test. They’re all fast, so just use Array.isArray — it’s well-supported now and works across frames.

Solution

In modern browsers you can do:

Array.isArray(obj)

(Supported by Chrome 5, Firefox 4.0, IE 9, Opera 10.5 and Safari 5)

For backward compatibility you can add the following:

// only implement if no native implementation is available
if (typeof Array.isArray === 'undefined') {
  Array.isArray = function(obj) {
    return Object.prototype.toString.call(obj) === '[object Array]';
  }
};

If you use jQuery you can use jQuery.isArray(obj) or $.isArray(obj). If you use underscore you can use _.isArray(obj).

If you don’t need to detect arrays created in different frames you can also just use instanceof:

obj instanceof Array

Answered By: Anonymous

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