javascript - Check if object is a jQuery object

The best way to check the instance of an object is through instanceof operator or with the method isPrototypeOf() which inspects if the prototype of an object is in another object's prototype chain.

obj instanceof jQuery;
jQuery.prototype.isPrototypeOf(obj);

But sometimes it might fail in the case of multiple jQuery instances on a document. As @Georgiy Ivankin mentioned:

if I have $ in my current namespace pointing to jQuery2 and I have an object from outer namespace (where $ is jQuery1) then I have no way to use instanceof for checking if that object is a jQuery object

One way to overcome that problem is by aliasing the jQuery object in a closure or IIFE

//aliases jQuery as $
(function($, undefined) {
    /*... your code */

    console.log(obj instanceof $);
    console.log($.prototype.isPrototypeOf(obj));

    /*... your code */
}(jQuery1));
//imports jQuery1

Other way to overcome that problem is by inquiring the jquery property in obj

'jquery' in obj

However, if you try to perform that checking with primitive values, it will throw an error, so you can modify the previous checking by ensuring obj to be an Object

'jquery' in Object(obj)

Although the previous way is not the safest (you can create the 'jquery' property in an object), we can improve the validation by working with both approaches:

if (obj instanceof jQuery || 'jquery' in Object(obj)) { }

The problem here is that any object can define a property jquery as own, so a better approach would be to ask in the prototype, and ensure that the object is not null or undefined

if (obj && (obj instanceof jQuery || obj.constructor.prototype.jquery)) { }

Due to coercion, the if statement will make short circuit by evaluating the && operator when obj is any of the falsy values (null, undefined, false, 0, ""), and then proceeds to perform the other validations.

Finally we can write an utility function:

function isjQuery(obj) {
  return (obj && (obj instanceof jQuery || obj.constructor.prototype.jquery));

}

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Let's take a look at: Logical Operators and truthy / falsy