关于js执行顺序
代码：,点击按钮，会执行js中的方法a()和b(),现在想让方法b()等待方法a()执行完再执行，该如何实现 。 （方法a（）其实是ajax调用的方法，方法b（）执行需要方法a（）的返回值）
------解决方案--------------------
把b()放在a()的if(xmlHttp.status == 200)里面。
------解决方案--------------------
把b()函数放a()函数最后面就行!
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