sample: detect elements with duplicate value by jQuery

HTML

<input value="20">
<input value="40">
<input value="10">
<input value="20">
<input value="30">
<input value="10">
<input value="10">

JavaScript

$("input").filter(function() {
	return $("input[value='" + this.value + "']").length > 1;
}).css("color", "#f00");