jquery detects whether a page element ID exists

Use the traditional JavaScript method as follows:

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if (document.getElementById (' div ')) { Find the corresponding element } else { No found the corresponding element found }

Using jquery is a simple matter of determining whether this element is 0 or not, and if 0 is not, the code is as follows:

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if ($ ("#div"). Length > 0) { Locate the element that corresponds to Id=div, and then execute this block of code }

You can even find a combination of elements, such as the following, we find an ID defined as the DIV element contains IMG, the code is as follows:

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if ($ ("#div img"). Length > 0) { Locate the element that corresponds to the ID=DIV and contains IMG, and then execute this block of code }

Cases

Taking ID=ABC as an example

$ (' #abc ') returns the JQuery object (details can refer to the jquery manual) regardless of the presence of ID=ABC elements on the page, so we cannot use if ($ (' #abc ')) to judge.

can use

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if ($ ("#abc"). Size () > 0) {} Or if ($ ("#abc"). Length > 0) {}

Finding child nodes based on parent node

jquery Children () returns the byte point of the matched object
Children () returns the Transposon mediated point of the matched object

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<p>one</p> <div id= "ch" > <span>two</span> </div> jquery Code and functionality: function JQ () { Alert ($ ("#ch"). Children (). HTML ()); } $ ("#ch"). Children ()

Get the object [<span>two</span>]. So the result of HTML () is "two"

Finding the parent node based on child nodes

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<div id= "ch" > <span>two</span> <span id= "SP" >three</span> </div>

jquery Code and functionality

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Jquery.ready ({     alert ($ ("#ch"). Children ("#sp"). html ()); }); $ ("#ch"). Children () Gets the object [<span>two</span><span id= sp >three</span>]. $ ("#ch"). Children ("#sp") filtered [<span id= sp >three</span>]