How can I detect if a selector returns null?

peirix_59242 0
Viewed 217535

What is the best way to detect if a jQuery-selector returns an empty object. If you do:

alert($('#notAnElement'));

you get [object Object], so the way I do it now is:

alert($('#notAnElement').get(0));

which will write "undefined", and so you can do a check for that. But it seems very bad. What other way is there?

jquery-selectors jquery
8 Answers

My favourite is to extend jQuery with this tiny convenience:

$.fn.exists = function () {
    return this.length !== 0;
}

Used like:

$("#notAnElement").exists();

More explicit than using length.

Magnar_11230 
if ( $("#anid").length ) {
  alert("element(s) found")
} 
else {
  alert("nothing found")
}
duckyflip_73700

The selector returns an array of jQuery objects. If no matching elements are found, it returns an empty array. You can check the .length of the collection returned by the selector or check whether the first array element is 'undefined'.

You can use any the following examples inside an IF statement and they all produce the same result. True, if the selector found a matching element, false otherwise.

$('#notAnElement').length > 0
$('#notAnElement').get(0) !== undefined
$('#notAnElement')[0] !== undefined
user_836670

You may want to do this all the time by default. I've been struggling to wrap the jquery function or jquery.fn.init method to do this without error, but you can make a simple change to the jquery source to do this. Included are some surrounding lines you can search for. I recommend searching jquery source for The jQuery object is actually just the init constructor 'enhanced'

var
  version = "3.3.1",

  // Define a local copy of jQuery
  jQuery = function( selector, context ) {

    // The jQuery object is actually just the init constructor 'enhanced'
    // Need init if jQuery is called (just allow error to be thrown if not included)
    var result = new jQuery.fn.init( selector, context );
    if ( result.length === 0 ) {
      if (window.console && console.warn && context !== 'failsafe') {
        if (selector != null) {
          console.warn(
            new Error('$(\''+selector+'\') selected nothing. Do $(sel, "failsafe") to silence warning. Context:'+context)
          );
        }
      }
    }
    return result;
  },

  // Support: Android <=4.0 only
  // Make sure we trim BOM and NBSP
  rtrim = /^[\s\uFEFF\xA0]+|[\s\uFEFF\xA0]+$/g;

jQuery.fn = jQuery.prototype = {

Last but not least, you can get the uncompressed jquery source code here: http://code.jquery.com/

user_5658770
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