如果就绪状态是 4 而且状态码是 200，就可以处理服务器的数据了，而且这些数据应该就是要求的数据（而不是错误或者其他有问题的信息）。

With a ready state of 4 and a status code of 200, you're ready to process the server's data and that data should be what you asked for (and not an error or other problematic piece of information).

youdao

如果出现这样的问题，您需要检查文件是否有漏掉逗号、大括号，或者出现其他语法错误。

If this problem is the case, check the file for missing commas, open braces, or any other syntax errors.

youdao

或者是其他错误？

Or is there something else?

youdao

hey'd rather single step it through using Idol or something, than just read it and try and figure things out. The most important thing to remember when you're doing all of this is to be systematic.

比起阅读代码发现错误来他们,宁愿用内置的操作层,或者其他工具一步完成,你要记住的最重要的事情,就是要系统化的去做调试。

麻省理工公开课 - 计算机科学及编程导论课程节选