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Why Do Event Handlers in JavaScript Loops Need Closures?

Barbara Streisand
Release： 2024-11-06 15:44:02
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Why Do Event Handlers in JavaScript Loops Need Closures?

Event Handlers within JavaScript Loops: The Need for Closures

In JavaScript, when working with event handlers within loops, it can be necessary to implement closures to ensure proper parameter passing. Consider the following code:

<code class="javascript">for (var i = 0; i < blah.length; i++) {
  var select = document.createElement('select');
  select.onchange = function() {
    onStatusChanged(select, callid, anotherid);
  };
}
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In this scenario, when the onchange event fires, the values passed to onStatusChanged() are consistent across all element), c (the current callid), and a (the current anotherid)

  • The closure immediately calls the function, passing in the current values of s, c, and a

    • When the onchange event fires, the closures execute, ensuring that onStatusChanged() receives the correct values for each