https://github.com/raganwald/jquery-predicates

.exists() and does_not_exist() for jQuery
https://github.com/raganwald/jquery-predicates

Last synced: 7 days ago
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.exists() and does_not_exist() for jQuery

• Host: GitHub
• URL: https://github.com/raganwald/jquery-predicates
• Owner: raganwald
• Created: 2010-09-14T04:27:23.000Z (about 14 years ago)
• Default Branch: master
• Last Pushed: 2012-10-15T14:12:11.000Z (about 12 years ago)
• Last Synced: 2023-04-12T08:06:54.271Z (over 1 year ago)
• Language: JavaScript
• Homepage:
• Size: 103 KB
• Stars: 16
• Watchers: 1
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

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README

        
jQuery Predicates

===

[jQuery Predicates][pred] adds two new methods to jQuery:

* **exists** returns true if the selection is not empty. For example, `$('.preference-pane:visible').exists()` returns true if the preference pane is visible.

* **do\_not\_exist** returns true if the selection is empty. For example, `$('input.invalid').do_not_exist()` returns true if there are no `input` elements with class `invalid`.

For your convenience, there are synonyms `.exist()` and `.does_not_exist()`, so your code can give a hint as to whether you expect there to be one or many elements. So you can write this:

    outstanding_tasks = $('.task.outstanding')

    if (outstanding_tasks.exist())

      update_to_do_list(outstanding_tasks);

    

Or perhaps this:

    while ($('.notification-banner').does_not_exist()) {

      // ...

    }

See for yourself:

    ;(function (jq_fn) {		

    	jq_fn.exists = function () {

    		return !!(this.length);

    	};

    	jq_fn.exist = jq_fn.exists;

    	jq_fn.do_not_exist = function () {

    		return !(this.length);

    	};

    	jq_fn.does_not_exist = jq_fn.do_not_exist;

    })(jQuery.fn);

    

If you don't want to use jQuery Predicates, by all means continue testing for `$('.foo:visible').length` or `$('input.invalid').length == 0`. But wouldn't you agree that it's more elegant to have code that says exactly what it means?

p.s. jQuery Predicates plays well with [jQuery Combinators][comb]'s `.ergo(...)` and `.when(..)` methods.

p.p.s I'm writing a book called [CoffeeScript Ristretto](http://leanpub.com/coffeescript-ristretto). Check it out!

[comb]: http://github.com/raganwald/jQuery-Combinators

[pred]: http://github.com/raganwald/jQuery-Predicates