HTML：

<input id="all" type="checkbox"/>全選
<hr />
<div>
	<input type="checkbox" class="box"/>
	<br/> 
	<input type="checkbox" class="box"/>
	<br/>
	<input type="checkbox" class="box"/>
	<br/>
	<input type="checkbox" class="box"/>
	<br/>
</div>
 

window.onload = function (){
	var all = document.getElementById ("all");			//全選checkbox
	var box = document.getElementsByClassName('box');	//子複選框
	
	//遍歷checkbox，把子複選框的checked設定成全選框的狀態，實現全選/全不選
	all.onclick = function (){
		for ( var i = 0; i < box.length; i++){
			box[i].checked = this.checked;
		}
	};
	//遍歷checkbox，子複選框有一個未選中時，如果全選框設為false不選狀態
	for ( var i = 0; i < box.length; i++){
		box[i].onclick = function (){
			if ( !this.checked ){
				all.checked = false;
			}
		};
	}
}