JQuery determines whether a page element exists

In traditional Javascript, it is best to determine whether a page element exists before performing some operations on a page element. The reason is that operations on a nonexistent element are not allowed.

For example:

document.getElementById("someID").innerHTML("hi");

If the element with ID "someID" does not exist, the Javascript running error: document. getElementById ("someID") is null.

The correct statement should be:

   obj = document.getElementById("someID");     if (obj){        obj.innerHTML("hi");     } 

In jQuery, how do we determine whether a page element exists or not? If we refer to the traditional Javascript writing method above, the first method we come up with must be:

if ($("#someID")){     $("#someID").text("hi"); } 

However, this is wrong! Because jQuery objects always return values, $ ("someID") is always TRUE, and IF statements do not have any judgment function. The correct statement should be:

    if ( $("#someID").length > 0 ) {         $("#someID").text("hi");      } 

Note: It is unnecessary for jQuery to determine whether a page element exists or not. jQuery will ignore the operation on a nonexistent element and will not report an error.

$(document).ready(function(){       var value=$('#btn_delXml').length;       if(value>0){           alert('Extsts');         }else {           alert('not Extsts');         } }) 

Summary:

When the jQuery selector gets the page element, an object is returned no matter whether the element exists or not. For example:

var my_element = $("#element_Id" )

At this time, the variable my_element is an object. Since it is an object, this object has the length attribute. Therefore, you can use the following code to determine whether an element (object) exists:

if(my_element.length>0){     alert("element is exist.");  }else{      alert("element not be found");  }