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

Question

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(option         


        

Answer 1

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?

Answer 2

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');
}

Answer 3

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.