The index method in jquery and the jqueryindex Method

The index method in jquery and the jqueryindex Method

Problem description:Flexible use of the index method in jquery

Method signature:Index ([selector | element])

Usage Overview:P1.index (P2) // The caller P1 can be an object or a set.

Instance used: 

<ul>    <li class="foo">Outer1</li>    <li>        <ul>            <li>1</li>            <li id="ok" class="foo">2</li>            <li>3</li>            <li class="foo">4</li>        </ul>    </li>    <li>Outer3</li></ul>

 

// Several test results
$ (". Foo "). index (); // 0 $ ("li "). index ("# OK"); //-1, cannot be found because $ ("li") is found in the element matching "# OK ") [0] $ ("li "). index ($ ("# OK"); // 3 $ ("li "). index (". foo "); // 0
// You can perform self-testing and research in more cases.

JQuery source code:(Recommended :)

// Determine the position of an element within// the matched set of elementsindex: function( elem ) {    // No argument, return index in parent    if ( !elem ) {        return ( this[ 0 ] && this[ 0 ].parentNode ) ? this.first().prevAll().length : -1;    }    // index in selector    if ( typeof elem === "string" ) {        return jQuery.inArray( this[ 0 ], jQuery( elem ) );    }    // Locate the position of the desired element    return jQuery.inArray(        // If it receives a jQuery object, the first element is used        elem.jquery ? elem[ 0 ] : elem, this );}