Question

在以下示例中，为什么不能从函数内部访问“ status.value”？如果我在函数内用document.getElementById（“ Label”）。value替换“ status.value”，则一切正常。谢谢。

<html>
<body onload="Ticker()">
 <label>Connection Status:</label>
 <input type="text" readonly="true" value="Idle" id="Label">
 <input type="button" value="Start/Stop" onclick="run=!run">
 <br>

 <script>
 var status = document.getElementById("Label");
 var run;

  function Ticker() {
      setTimeout( Ticker, 100 );

        if(run){
           status.value = "Connected";
        }else{
           status.value = "Disconnected";
        }
  }
</script>
</body>
</html>

Answer 1

<html>

  <body onload="Ticker()">
    <label>Connection Status:</label>
    <input type="text" readonly="true" value="Idle" id="Label">
    <input type="button" value="Start/Stop" onclick="run=!run">
    <br>

    <script>
      var run;

      function Ticker() {
        setTimeout(Ticker, 100);
        var status = document.getElementById("Label");
        if (run) {
          status.value = "Connected";
        } else {
          status.value = "Disconnected";
        }
      }

    </script>
  </body>

</html>

Answer 2

由于计时器下的功能在下一个事件周期中执行，因此不会知道状态。如果要传递“状态”，则应将其作为参数传递给settimeout函数，如下所示：-

 var status = document.getElementById("Label");
function Ticker(status) {
        setTimeout(Ticker, 100,status);      
        if (run) {
          status.value = "Connected";
        } else {
          status.value = "Disconnected";
        }
      }

getElementById变量作用域

2 个答案: