Js/jquery determine if a DOM node exists

JS Native judge whether the DOM node exists in the page

The JavaScript native function does not provide a way to judge whether a DOM node exists, and we usually get DOM nodes that are almost document.getelement. Method, a set of object numbers is returned, and we can access each object of the collection through object[0],object[1]. Since the return is a set of numbers, then there is the length property, and length greater than or equal to 1 means that the DOM node exists in the page

Code:

function () {     if(typeofthis. Length>=1)        {return  true;    }      return false ;};

Use:

Assume that the page has the following node

<div> Here is the div node </div><div> here is the div node </div><span> here is the span node </span>

Determine if the node is on the page:

var is_exist = document.getelementsbytagname (' div '). exist (); alert (is_exist);     // true var is_exist = document.getElementsByTagName (' span '). exist (); alert (is_exist);     // true var is_exist = document.getElementsByTagName (' P '). exist (); alert (is_exist);     // false

Note: If you use the document.getElementById () method to get an object, you cannot use the exist () method, because the method that takes the node object by ID returns an empty object without a node, and does not integrate the prototype exist () function. So it will be an error! So if the object is based on the ID can be directly if (obj) so as to determine whether the DOM node exists in the page

jquery determines if a DOM node exists in the page

You can do this.

To add a prototype:

(function($) {    function() {        if($ (this). length>= 1) {            returntrue;        }         return false ;    };}) (jQuery);

How to use:

If the page has the following DOM node to judge:

<div id= "A" > here is the id=a node </div><div> here is the div node </div><div> here is the div node </div><span > Here is the span node </span>

// false // true // true // false

Both of these methods actually determine whether an object exists based on the length property of the object collection.

Js/jquery determine if a DOM node exists