Because jQuery's implementation of :nth- selectors is strictly derived from the CSS specification, the value of n is "1-indexed", meaning that the counting starts at 1. For other selector expressions such as :eq() or :even jQuery follows JavaScript's "0-indexed" counting. Given a single <ul> containing two <li>s, $( "li:nth-child(1)" ) selects the first <li> while $( "li:eq(1)" ) selects the second.
The :nth-child(n) pseudo-class is easily confused with :eq(n), even though the two can result in dramatically different matched elements. With :nth-child(n), all children are counted, regardless of what they are, and the specified element is selected only if it matches the selector attached to the pseudo-class. With :eq(n) only the selector attached to the pseudo-class is counted, not limited to children of any other element, and the (n+1)th one (n is 0-based) is selected.
Further discussion of this unusual usage can be found in the W3C CSS specification.
Find the second li in each matched ul and note it.
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>nth-child demo</title>
<style>
div {
float: left;
}
span {
color: blue;
}
</style>
<script src="https://code.jquery.com/jquery-1.10.2.js"></script>
</head>
<body>
<div>
<ul>
<li>John</li>
<li>Karl</li>
<li>Brandon</li>
</ul>
</div>
<div>
<ul>
<li>Sam</li>
</ul>
</div>
<div>
<ul>
<li>Glen</li>
<li>Tane</li>
<li>Ralph</li>
<li>David</li>
</ul>
</div>
<script>
$( "ul li:nth-child(2)" ).append( "<span> - 2nd!</span>" );
</script>
</body>
</html>
This is a playground to see how the selector works with different strings. Notice that this is different from the :even and :odd which have no regard for parent and just filter the list of elements to every other one. The :nth-child, however, counts the index of the child to its particular parent. In any case, it's easier to see than explain so...
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>nth-child demo</title>
<style>
button {
display: block;
font-size: 12px;
width: 100px;
}
div {
float: left;
margin: 10px;
font-size: 10px;
border: 1px solid black;
}
span {
color: blue;
font-size: 18px;
}
#inner {
color: red;
}
td {
width: 50px;
text-align: center;
}
</style>
<script src="https://code.jquery.com/jquery-1.10.2.js"></script>
</head>
<body>
<div>
<button>:nth-child(even)</button>
<button>:nth-child(odd)</button>
<button>:nth-child(3n)</button>
<button>:nth-child(2)</button>
</div>
<div>
<button>:nth-child(3n+1)</button>
<button>:nth-child(3n+2)</button>
<button>:even</button>
<button>:odd</button>
</div>
<div>
<table>
<tr><td>John</td></tr>
<tr><td>Karl</td></tr>
<tr><td>Brandon</td></tr>
<tr><td>Benjamin</td></tr>
</table>
</div>
<div>
<table>
<tr><td>Sam</td></tr>
</table>
</div>
<div>
<table>
<tr><td>Glen</td></tr>
<tr><td>Tane</td></tr>
<tr><td>Ralph</td></tr>
<tr><td>David</td></tr>
<tr><td>Mike</td></tr>
<tr><td>Dan</td></tr>
</table>
</div>
<span>tr<span id="inner"></span></span>
<script>
$( "button" ).click(function() {
var str = $( this ).text();
$( "tr" ).css( "background", "white" );
$( "tr" + str ).css( "background", "#ff0000" );
$( "#inner" ).text( str );
});
</script>
</body>
</html>
Please login to continue.