How do you check if a selector matches something in jQuery? [duplicate]

问题

In Mootools, I'd just run if ($('target')) { ... }. Does if ($('#target')) { ... } in jQuery work the same way?

回答1:

As the other commenters are suggesting the most efficient way to do it seems to be:

if ($(selector).length ) {
    // Do something
}

If you absolutely must have an exists() function - which will be slower- you can do:

jQuery.fn.exists = function(){return this.length>0;}

Then in your code you can use

if ($(selector).exists()) {
    // Do something
}

As answered here

回答2:

no, jquery always returns a jquery object regardless if a selector was matched or not. You need to use .length

if ( $('#someDiv').length ){

}

回答3:

if you used:

jQuery.fn.exists = function(){return ($(this).length > 0);}
if ($(selector).exists()) { }

you would imply that chaining was possible when it is not.

This would be better

jQuery.exists = function(selector) {return ($(selector).length > 0);}
if ($.exists(selector)) { }

回答4:

I think most of the people replying here didn't quite understand the question, or else I might be mistaken.

The question is "how to check whether or not a selector exists in jQuery."

Most people have taken this for "how to check whether an element exists in the DOM using jQuery." Hardly interchangeable.

jQuery allows you to create custom selectors, but see here what happens when you try to use on e before initializing it;

$(':YEAH');
"Syntax error, unrecognized expression: YEAH"

After running into this, I realized it was simply a matter of checking

if ($.expr[':']['YEAH']) {
    // Query for your :YEAH selector with ease of mind.
}

Cheers.

回答5:

Yet another way:

$('#elem').each(function(){
  // do stuff
});

回答6:

if ($('#elem')[0]) {
  // do stuff
}

回答7:

Alternatively:

if( jQuery('#elem').get(0) ) {}

回答8:

I prefer the

    if (jQuery("#anyElement").is("*")){...}

Which basically checks if this elements is a kind of "*" (any element). Just a cleaner syntax and the "is" makes more sense inside an "if"

回答9:

jQuery.fn.exists = function(selector, callback) {
    var $this = $(this);
    $this.each(function() {
        callback.call(this, ($(this).find(selector).length > 0));
    });
};

回答10:

For me .exists doesn't work, so I use the index :

if ($("#elem").index() ! = -1) {}

回答11:

firstly create a function:

$.fn.is_exists = function(){ return document.getElementById(selector) }

then

if($(selector).is_exists()){ ... }

来源：https://stackoverflow.com/questions/299802/how-do-you-check-if-a-selector-matches-something-in-jquery

标签

javascript

jquery

jquery-selectors