javascript - Check if object is a jQuery object

Is there a fast way of checking if an object is a jQuery object or a native JavaScript object?

example:

var o = {};
var e = $('#element');

function doStuff(o) {
    if (o.selector) {

        console.log('object is jQuery');
    }
}

doStuff(o);
doStuff(e);

obviously, the code above works but it's not safe. You could potentially add a selector key to the o object and get the same result. Is there a better way of making sure that the object actually is a jQuery object?

Something in line with (typeof obj == 'jquery')

Answer

You can use the instanceof operator:

obj instanceof jQuery

Explanation: the jQuery function (aka $) is implemented as a constructor function. Constructor functions are to be called with the new prefix.

When you call $(foo), internally jQuery translates this to new jQuery(foo)¹. JavaScript proceeds to initialize this inside the constructor function to point to a new instance of jQuery, setting it's properties to those found on jQuery.prototype (aka jQuery.fn). Thus, you get a new object where instanceof jQuery is true.

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¹_{It's actually new jQuery.prototype.init(foo): the constructor logic has been offloaded to another constructor function called init, but the concept is the same.}