js控制checkbox全选取消全选

<label for=""><span>1</span><input type="checkbox" value="1"></label> <label for=""><span>2</span><input type="checkbox" value="2"></label> <label for=""><span>3</span><input type="checkbox" value="3"></label> <label for=""><span>4</span><input type="checkbox" value="4"></label> <label for=""><span>4</span><input type="text" value="5"></label> <button>全选/取消全选</button> <script> var oBtn = document.getElementsByTagName("button")[0]; var flag = false; oBtn.onclick = function(){ var oTxt = document.querySelectorAll("input[type='checkbox']"); if(!flag){ for (var i = 0; i < oTxt.length; i++) { oTxt[i].checked = true; } flag = true; }else{ for (var i = 0; i < oTxt.length; i++) { oTxt[i].checked = false; } flag = false; } } </script>