To do this, make a HEAD request and then check for a 404 error in your callback function; Listing 11 shows a sample callback.

要实现这种功能，生成一个HEAD请求，然后在回调函数中检查404错误；清单11给出了一个简单的回调函数。

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The first difference, therefore, is a result of our attempt to make the sample application easy to test, and has no significance to the design of the solution for the Claim Check pattern.

因此，第一个区别是由于我们尝试使样例应用程序易于测试而出现的，且它对Claim Check模式解决方案的设计没有任何意义。

youdao

The first difference, therefore, is a result of our attempt to make the sample application easy to test, and has no significance to the design of the solution for the Claim Check pattern.

因此，第一个区别是由于我们尝试使样例应用程序易于测试而出现的，且它对Claim Check模式解决方案的设计没有任何意义。

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