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怎么理解JavaScript中的window.a和a?

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怎么理解JavaScript中的window.a和a?

如图:
image.png

为什么JavaScript会有这种行为?
背后涉及到什么原理?

望解答.
也可以给出相关知识点,真的想弄明白为啥会这样啊??
??????


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by (71.8m points)
  1. 首先 window 是浏览器环境的 global 环境
  2. a 这样是在执行环境上下文开始向上查找，如果找到 global 都找不到就会报错
  3. window.a 这样等于从 window 对象上访问 a

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