Check If Object Is a Jquery Object

Check if object is a jQuery object

You can use the instanceof operator:

if (obj instanceof jQuery){
    console.log('object is 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.}

How to detect is argument jQuery object

Use the typeof operator

if ( typeof value === 'string' ) {
  // it's a string
} else {
  // it's something else
}

Or to make really sure it's an instance of the jQuery object

if ( typeof value === 'string' ) {
  // it's a string
} else if ( value instanceof $) {
  // it's a jQuery object
} else {
  // something unwanted
}

How to check if an object is a jQuery event

Agreeing @Rocket's comment: instanceof is the way to go. You can try this on SO's website in the JS console

var x = $.Event()
x instanceof $.Event

More information can be found in this eerily similar post: https://stackoverflow.com/a/1853246/1883547

jQuery - check if variable is dom element

You can use instanceof to check if the object passed in is an instanceof jQuery or an instanceof HTMLElement. If it is return true;. Otherwise, return false.

function isDomElem(obj) {
      if(obj instanceof HTMLCollection && obj.length) {
          for(var a = 0, len = obj.length; a < len; a++) {
              if(!checkInstance(obj[a])) {
                  console.log(a);
                  return false;   
              }
          }     
          return true;                
      } else {
          return checkInstance(obj);  
      }

      function checkInstance(elem) {
          if((elem instanceof jQuery && elem.length) || elem instanceof HTMLElement) {
              return true;  
          }
          return false;        
      }
}

Optionally, instead of returning true or false, you could do some other action. You could also split each option out and do a separate action depending on which one the object is an instance of jQuery or HTMLElement. You have lots of choices to choose from.

$(function () {  var temp1 = $('div'),      temp2 = $('div')[0],      temp3 = "foo",      temp4 = ['bar'],      temp5 = $('span'),      temp6 = document.getElementsByClassName("test");    alert(isDomElem(temp1));  alert(isDomElem(temp2));  alert(isDomElem(temp3));  alert(isDomElem(temp4));  alert(isDomElem(temp5));  alert(isDomElem(temp6));    function isDomElem(obj) {          if(obj instanceof HTMLCollection && obj.length) {                for(var a = 0, len = obj.length; a < len; a++) {            if(!checkInstance(obj[a])) {                return false;               }        }                       return true;                     } else {          return checkInstance(obj);        }              function checkInstance(elem) {          if((elem instanceof jQuery && elem.length) || elem instanceof HTMLElement) {              return true;            }          return false;              }  }});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script><div></div><p class="test"></p><p class="test"></p>

Is there an exists function for jQuery?

In JavaScript, everything is 'truthy' or 'falsy', and for numbers 0 means false, everything else true. So you could write:

if ($(selector).length)

You don't need that >0 part.

How to know an object is jQuery object or not

Use instanceof:

console.log(elm instanceof jQuery);

or:

console.log(elm instanceof $);

Demo: http://jsfiddle.net/karim79/8jUKX/

Check if JQuery object exists in DOM

If performance is a really big concern for you, native methods are generally the way to go.

document.contains($myJQueryEl[0])

Outperforms the next fastest jQuery operation, $elem.closest('body'), by around 4 times according to this answer and its comment.

If you're really looking for performance for non-document elements, however, Shadow DOM is definitely your best option.

Determine if a variable is an empty jquery object

$targetSection.length will be zero if no matching selector is found.

How can I determine if a jQuery object is deferred?

Depending on your use case, you could also use jQuery.when [1]:

If a single argument is passed to jQuery.when and it is not a Deferred, it will be treated as a resolved Deferred and any doneCallbacks attached will be executed immediately.

With jQuery.when you can treat your mysterious object always as deferred:

// x could be a deferred object or an immediate result
var x = getMysteriousObject();
// success will be called when x is a deferred object and has been resolved
// or when x is an immediate result
jQuery.when( x ).then( success, error );

[1] http://api.jquery.com/jQuery.when/

How do I check if a variable is a jQuery object or plain DOM element?

• A jquery object has a jquery property.
• A jquery object is an instanceof jQuery (instanceof on MDN)
• A DOM element has a nodeType property

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