CODEWITHSUNDEEP
javascriptargumentsargument-passing
zero
zero

Reputation: 3084

How to check if an argument is an object (and not an array) in JavaScript

After testing out instasnceof I found that it will return true if the argument is an array or an object literal.

function test(options){
  if(options instanceof Object){alert('yes')}//this will alert for both arrays and object literals
}
test({x:11})// alerts
test([11])// alerts as well but I do not want it to

Is there a way to test if the argument "options" is an object literal?

P.S. I am creating a module that will allow the user to access its configuration options, and I want to test if the argument is only an object literal or not?

Upvotes: 3

Views: 5600

Answers (4)

James Porter
James Porter

Reputation: 183

An alternative solution would be to use Lodash:

_.isPlainObject(value)

Here is the documentation: https://lodash.com/docs/4.17.15#isPlainObject

Upvotes: 0

T.J. Crowder
T.J. Crowder

Reputation: 1074505

is there a way to test if the argument "options" is an object literal?

No, because it makes no sense. You can test whether it's an object, but how it was created (via a literal in the call to your function, via a literal elsewhere, through new Object, by deserializing a JSON string, ...) is not information that's maintained.

after testing out instasnceof i found that it will return true if the argument is an array or an object literal

Correct. Arrays in JavaScript are objects (and not really arrays).

If you want to test that an object is a plain old object, you can do this:

if (Object.prototype.toString.call(options) === "[object Object]") {
    // It's a plain object
}

But there's really no reason to do that. It's not your problem. As long as what they pass you has the properties you expect, don't try to limit the object further.

p.s. i'm making a module that will allow the user to pass it configuration options and i want to test to make sure that the argument is only an object literal.

Why? If the user wants to use an object that hasn't been declared as a literal right there and then, why would you care? If they want to use an object that they've created via a different constructor function (e.g., rather than just a plain object), again, why would you care?

Upvotes: 12

Bergi
Bergi

Reputation: 664620

function isPlainObject(o) {
     return Object(o) === o && Object.getPrototypeOf(o) === Object.prototype;
}

However, you can't test wether o was declared as a literal or instantiated somehow else - you can just test whether it's a plain object without any constructor than Object.

Upvotes: 2

Paul Phillips
Paul Phillips

Reputation: 6259

If you're trying to forbid arrays, you can just do this:

var isObject = options instanceof Object;
var isArray = options instanceof Array;
if(isObject && !isArray)
{
    alert('yes');
}

Upvotes: 1

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