在本演练中，将使用调试器，它使您可以逐行通过页面代码，并检查变量值。

In this walkthrough, you will work with the debugger, which allows you to step through the page's code line by line and examine the values of variables.

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首先，从编程的观点来看，它从来不会检查变量值是否有效，如果激活警告信息，这就是要注意的一个因素。

From a programming perspective, it has the issue that it never checks if any of the variables have a valid value, a fact that would be highlighted if warnings were switched on.

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