Javascript的引用顺序 [英] Javascript order of referencing

问题描述

以下语句的运行顺序是什么？运行时是从右到左执行它吗？

What order does the following statement run? Does the runtime execute it from right to left?

  length = i = test = output = null;

推荐答案

是的，因为分配表达式不是左手边的表达本身，嵌套是

Yes, since an assignment expression is not a lefthand-side expression itself, the nesting is

(length = (i = (test = (output = null))));

从外向内执行，从左到右解决引用（首先获得 length 变量，然后评估右侧，即获取 i 变量并评估...）。这意味着输出是第一个被分配的变量，然后是 test ，然后是 i ，最后长度：从右到左，如果你愿意的话。由于赋值运算符总是产生其右操作数，因此所有内容都将被赋予相同的（最里面的，最右边的）值： null 。

It is executed from outside-in, solving references left-to-right (first getting the length variable, then evaluating the right side, which is getting the i variable and evaluating …). That means output is the first variable that is getting assigned to, then test, then i, and last length: "right-to-left" if you want. Since the assignment operator always yields its right operand, everything will be assigned the same (innermost, rightmost) value: null.

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