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。

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