:first-child Selector
first-child selector
version added: 1.1.4jQuery(':first-child')
描述： 选择所有父级元素下的第一个子元素。
虽然:first只匹配一个单独的元素，但是:first-child选择器可以匹配超过一个：为每个父级元素匹配第一个子元素。这相当于:nth-child(1)。
Example:
Finds the first span in each matched div to underline and add a hover state.
<!DOCTYPE html>
<html>
<head>
<style>
span { color:#008; }
span.sogreen { color:green; font-weight: bolder; }
</style>
<script src="http://code.jquery.com/jquery-latest.min.js"></script>
</head>
<body>
<div>
<span>John,</span>
<span>Karl,</span>
<span>Brandon</span>
</div>
<div>
<span>Glen,</span>
<span>Tane,</span>
<span>Ralph</span>
</div>
<script>
$("div span:first-child")
.css("text-decoration", "underline")
.hover(function () {
$(this).addClass("sogreen");
}, function () {
$(this).removeClass("sogreen");
});
</script>
</body>
</html>