javascript - false in addEventListener?

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javascript - false in addEventListener?

asked Jan 31, 2022 in Technique[技术] by 深蓝 (71.8m points)

in this below line: third parameter is kept false. what is this attribute??

var el = document.getElementById("outside");
el.addEventListener("click", modifyText, false);

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1 Answer

深蓝 · Answer 1 · 2022-01-31T07:23:38+0000

It controls if the event will bubble up or down the DOM tree.

Click on three in the example below (and linked here). Then change false to true and repeat.

If useCapture is set to false, it will bubble up the tree and you will get x3, x2, x1, if it is set to true, it will bubble down and you will get x1, x2, x3.

See:

<!DOCTYPE html>
<html>
<head>
<meta charset=utf-8 />
<title>JS Bin</title>
</head>
<body>
  <div id="x1">One
    <div id="x2">Two
      <div id="x3">Three
      </div>
    </div>
  </div>
  <script>
    function me() { alert(this.id); };
    var divs = document.getElementsByTagName('div');
    for (var i = 0; i < divs.length; i++) {
      divs[i].addEventListener('click', me, false);
    }
  </script>
</body>
</html>

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