Why does Javascript's regex.exec() not always return the same value? [duplicate]

问题：

This question already has an answer here: 这个问题在这里已有答案：

• Why does a RegExp with global flag give wrong results? 为什么带有全局标志的RegExp会产生错误的结果？ 6 answers 6个答案

In the Chrome or Firebug console: 在Chrome或Firebug控制台中：

reg = /ab/g
str = "abc"
reg.exec(str)
   ==> ["ab"]
reg.exec(str)
   ==> null
reg.exec(str)
   ==> ["ab"]
reg.exec(str)
   ==> null

Is exec somehow stateful and depends on what it returned the previous time? exec在某种程度上是有状态的，取决于它之前返回的内容吗？ Or is this just a bug? 或者这只是一个错误？ I can't get it to happen all the time. 我无法让它一直发生。 For example, if 'str' above were "abc abc" it doesn't happen. 例如，如果上面的'str'是“abc abc”，则不会发生。

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解决方案：

参考： https://stackoom.com/en/question/m9nb