為什麼 Internet Explorer 會拋出「控制台未定義」錯誤以及如何修復它們？

IE's Undefined 'console': A Solution

Encountering "console is undefined" errors while debugging your web page in Internet Explorer can be frustrating. Here's a comprehensive guide to resolve this issue and prevent script errors effectively.

Problem Background

Firebug is an excellent tool for monitoring your code, but certain statements like "console.log(...)" may trigger runtime errors in IE8 and older versions. This is because IE lacks a native console object, leading to the "console is undefined" issue.

Initial Attempt

Attempts to patch this issue by defining a mock console object with a placeholder "log" function like this:

<script type="text/javascript">
    if (!console) console = {log: function() {}};
</script>

may not suffice. IE seems to interpret such code correctly but still throws the "console is undefined" error.

A Proven Solution

To eliminate these errors effectively, try this modified approach:

<script type="text/javascript">
    if (!window.console) console = {log: function() {}};
</script>

This revised method proves more reliable because it checks the 'window.console' attribute instead of directly accessing 'console.' An undefined variable cannot be referred to directly, but accessing an undefined attribute of a global context (window in browsers) is acceptable.

Alternative Option

If you prefer to steer clear of the 'window' variable, you can use this alternative:

<script type="text/javascript">
    if (typeof console === 'undefined') console = {log: function() {}};
</script>

This option accomplishes the same result effectively.

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