JavaScript``let''的说明和for循环的块作用域

这只是ES6的语法糖吗？

不，它不仅仅是语法糖。详细资料埋在§13.6.3.9中

CreatePerIterationEnvironment

这如何运作？

如果

let

for

• 使用以下名称创建一个新的词法环境：a）初始化程序表达式b）每次迭代（以前是评估增量表达式）
• 将具有这些名称的所有变量的值从一个复制到下一个环境

您的循环语句

for (var i = 0; i < 10; i++) process.nextTick(_ =>console.log(i));

// omitting braces when they don't introduce a blockvar i;i = 0;if (i < 10)    process.nextTick(_ => console.log(i))    i++;    if (i < 10)        process.nextTick(_ => console.log(i))        i++;        …

while

for (let i = 0; i < 10; i++) process.nextTick(_ => console.log(i));

// using braces to explicitly denote block scopes,// using indentation for control flow{ let i;  i = 0;  __status = {i};}{ let {i} = __status;  if (i < 10)      process.nextTick(_ => console.log(i))      __status = {i};}   { let {i} = __status;      i++;      if (i < 10)          process.nextTick(_ => console.log(i))          __status = {i};    }   { let {i} = __status;          i++;          …