在JavaScript中，什么代码在运行时执行，哪些代码在分析时执行？ [英] In JavaScript, what code executes at runtime and what code executes at parsetime?

问题描述

特别是对象，我不明白对象的哪些部分在初始化之前运行，什么在初始化时运行以及什么时候运行。

With objects especially, I don't understand what parts of the object run before initialization, what runs at initialization and what runs sometime after.

编辑：似乎那个解析时间错了。我想我应该制定一个问题在2遍读取中，第一遍读取什么，第二遍读取什么？

It seems that parsetime is the wrong word. I guess I should have formulated the question "In the 2-pass read, what gets read the first pass and what gets read the second pass?"

推荐答案

javascript文件以2遍读取方式运行。第一遍解析语法并收集函数定义，第二遍实际执行代码。通过注意以下代码可以看出这一点：

A javascript file is run in a 2-pass read. The first pass parses syntax and collects function definitions, and the second pass actually executes the code. This can be seen by noting that the following code works:

foo();

function foo() {
  return 5;
}

但以下不是

foo(); // ReferenceError: foo is not defined

foo = function() {
  return 5;
}

然而，这并不是很有用，因为没有第一遍中的任何执行。您无法使用此功能来更改逻辑。

However, this isn't really useful to know, as there isn't any execution in the first pass. You can't make use of this feature to change your logic at all.

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