Jquery method to determine whether the object obtained by $('#id') exists_jquery

1. Determine whether the object exists

If the following jQuery code is used to determine whether an object exists, it cannot be used

Copy code The code is as follows:

if($("#id")){
}else{}

Because $(“#id”) will return object regardless of whether the object exists.

To correctly determine whether an object exists, you should use:

Copy the code The code is as follows:

if($("#id").length>0){}else{}

Use the length property of the jQuery object to determine, if > 0 exists.

or

Copy code The code is as follows:

if($(" #id")[0]){} else {}

Or directly use the native Javascript code to judge:

Copy code The code is as follows:

if(document.getElementById("id")){} else {}

2. Find child nodes based on the parent node
jQuery's children() returns the byte point of the matching object
children() returns the child point of the matching object

Copy code The code is as follows:

one

two

jQuery code and functions:
function jq(){
alert($(“#ch”).children(). html());
}
$("#ch").children() gets the object [ two ]. So the result of .html() is "two"
[code]
3. Find the parent node based on the child node
[code]

two
three

jQuery code and functions

Copy code The code is as follows:

Jquery.ready ({
alert($(“#ch”).children(“ #sp”).html());
});
$(“#ch”).children() gets the object [twothree ].
$("#ch").children("#sp") filters to get [three ]