js 多選框

js實作多選框的全選

<form action="" method="post">
			<input type="checkbox" id="first" /><br>
			<input type="checkbox" name="aihao" value="唱歌" />唱歌 <br>
			<input type="checkbox" name="aihao" value="跳舞" />跳舞 <br>
			<input type="checkbox" name="aihao" value="睡覺" />睡覺 <br>
			<input type="button"  id="submit" value="送出" />
		</form>

		<script type="text/javascript">
			var first = document.getElementById('first');
			var aihaos = document.getElementsByName('aihao');

			first.onclick = function() {
				for (var i = 0; i < aihaos.length; i++) {
					aihaos[i].checked = first.checked;
				}
			}
			//當都被選中時，複選框也被選中
			var all = aihaos.length;
			for (var i = 0; i < aihaos.length; i++) {
				console.log('for循環')
				aihaos[i].onclick = function() {
					var count = 0;
					for (var j = 0; j < aihaos.length; j++) {
						console.log('j='+j);
						if (aihaos[j].checked) {
							count++;
						}
					}
					console.log(count);
					first.checked = (all == count);
				}
			}
			//送出value值，為一個String數組
			var submit =	 document.getElementById('submit');
			submit.onclick = function () {
				var arr = [];
				for (var i = 0; i < aihaos.length; i++) {
					if (aihaos[i].checked) {
						arr.push(aihaos[i].value) 
					}
				}
				console.log(arr);
			}
			
		</script>