JQuery-Is () method

Definition and Usage:

Detects a collection of matching elements based on a selector, DOM element, or JQuery object, and returns true if at least one of the elements conforms to the given expression. Returns ' false ' if no element is met, or if the expression is not valid. "Note:" in jquery 1.3, all expressions are supported. In previous releases, a complex expression, such as a hierarchy selector (such as +, ~ and >), would always return true

Detailed Description:
Unlike other filtering methods,. is () does not create a new JQuery object. Instead, it allows us to detect the contents of a JQuery object without modifying it. This is often useful inside callback, such as event handlers.

For example, suppose we have a list where two items contain child elements, you can add a click handler to the <ul> element, and then limit the code to trigger only if the list item itself, not the child element, is clicked.

1<! DOCTYPE html>234<script type= "Text/javascript" src= "/jquery/jquery.js" ></script>56 7<body>8<ul>9<li>list <strong>item 1</strong></li>Ten<li><span>list Item 2</span></li> One<li>list Item 3</li> A</ul> -  -<script> the$ ("ul"). Click (function(event) { -   var$target =$ (event.target); -   if($target. Is ("Li") ) { -$target. CSS ("Background-color", "Red"); +   } - }); +</script> A  at</body> -

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When you click on the word "list" in the first list item or any word in the third list item, the clicked list item is set to the red background. However, when a user clicks on any word in Item 1 or the second list item in the first list item, there is no change, because in this case, the objective of the event is <strong> is <span>.
　　Note: for selector expression strings with a positional selector, such as: First,: GT () or: Even, positional filtering is for the JQuery object passed to. is (), not for the containing document. So for the above HTML, such as $ ("Li:first"). The expression of IS ("Li:last") returns True, but $ ("Li:first-child"). Is ("Li:last-child") returns false.

Using functions

The second use of this method is to evaluate an expression that is based on a function rather than a related element of the selector. For each element, if the function returns True, then. is () also returns True. For example, here is a slightly more complex HTML fragment,

You can add a click handler to each <li> to calculate the number of <li> internal <strong> elements that are clicked:

1<! DOCTYPE html>234<script type= "Text/javascript" src= "/jquery/jquery.js" ></script>56 7<body>8<ul>9<li><strong>list</strong> Item 1-one Strong tag</li>Ten<li><strong>list</strong> Item <strong>2</strong>- One<span>strong tags</span></li> A<li>list Item 3</li> -<li>list Item 4</li> -<li>list Item 5</li> the</ul> -  -<script> -$ ("Li"). Click (function() { +   var$li = $ ( This), -Iswithtwo = $li. Is (function() { +       return$ (' strong ', This). length = = 2; A     }); at   if(iswithtwo) { -$li. CSS ("Background-color", "green"); -}Else { -$li. CSS ("Background-color", "Red"); -   } - }); in</script> -  to</body> +

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The IS () function compares common uses:

1     //whether it is hidden2$ (' #test '). Is (': Visible '));3     //determines whether the INPUT element is selected4$ (' input[name=chknochecked] '). Is (': Checked '));5     //whether it is the first child element6$( This). Is (": First-child");7     //whether to include the. Blue,.red class8$( This). is (". blue,.red");9     //does the text contain the word Peter ?Ten$( This). Is (": Contains (' Peter ')");

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Reference:

JQUERY is ()

JQuery traversal-is () method

JQuery-Is () method