<html>
<script language=javascript>
function selectAll(){
var a = document.getElementsByTagName("input");
if(a[0].checked){
for(var i = 0;i<a.length;i++){
if(a[i].type == "checkbox") a[i].checked = false;
}
}
else{
for(var i = 0;i<a.length;i++){
if(a[i].type == "checkbox") a[i].checked = true;
}
}
}
</script>
<input type="checkbox" value=1 />
<input type="checkbox" value=2 />
<input type="checkbox" value=3 />
<input type="checkbox" value=4 />
<input type="checkbox" value=5 />
<input type="button" name="select" onclick="selectAll()" value="全选/全不选"/>
</html>
原文：http://www.cnblogs.com/costa92/p/4060109.html