Using the is() method to return a Boolean value
It is often necessary to determine if the selected set of elements does, in fact, contain a specific element. Using the is() method, we can check the current set against an expression / filter. The check will return true if the set contains at least one element that is selected by the given expression / filter. If it does not contain the element, a false value is returned. Examine the following code:
Sample: sample23. html
<! DOCTYPE html > < html lang =" en "> < body > < div id =" i0 "> jQuery </ div > < div id =" i1 "> jQuery </ div > < script src =" http:// ajax. googleapis. com / ajax / libs / jquery / 1.7.2 / jquery. min. js "></ script >
< script >( function($){ // Returns true. alert($(' div '). is('# i1 ')); // Returns false. Wrapper set contains no < div > with id =" i2 ". alert($(' div '). is('# i2 ')); // Returns false. Wrapper set contains no hidden < div > alert($(' div '). is(': hidden '));
})( jQuery); </ script > </ body > </ html >
It should be apparent that the second alert() will return a value of false because our wrapper set did not contain a < div > that had an id attribute value of i2. The is() method is quite handy for determining if the wrapper set contains a specific element.
Notes: As of jQuery 1.3, the is() method supports all expressions. Previously, complex expressions such as those containing hierarchy selectors( such as +, ~, and >) always returned true. Filter is used by other internal jQuery functions. Therefore, all rules that apply there, apply here, as well. Some developers use is('. class ') to determine if an element has a specific class. Don ' t forget that jQuery already has a method for doing this called hasClass(' class '), which can be used on elements that contain more than one class value. But truth be told, hasClass() is just a convenient wrapper for the is() method.
35