javascript - JS lambda默认返回值

Question

我对 Node.js 中 lambda 的默认返回值有点困惑。我找到了这个链接"Arrow Functions" :

Arrow functions can have either a "concise body" or the usual "block body".

In a concise body, only an expression is specified, which becomes the implicit return value. In a block body, you must use an explicit return statement.

var func = x => x * x;                  
// concise body syntax, implied "return"

var func = (x, y) => { return x + y; }; 
// with block body, explicit "return" needed

这很清楚，但后来我发现了这段 Express 代码，我测试了它默认返回最后一条语句，而不需要使用“return”:

const express = require('express');
const app = express();

app.use('/api/posts', (req, res, next) => {
  const posts = [
    {
      id: 'sdfj234j654j',
      title: 'First server-side post',
      content: 'This is comming from the server'
    },
    {
      id: '9054jk4ju59u90o',
      title: 'Second server-side post',
      content: 'This is comming from the server!'
    }
  ];
  // this is returned by default and does not require "return "
  res.status(200).json({
    message: 'Posts fetched succesfully!',
    posts: posts
  });
});

那么当我使用 block 引号来定义 lambda 时，我需要使用哪一个 return 语句呢？还是有我不知道的异常(exception)情况？

Answer 1

示例中的箭头函数不返回任何内容。然而，它通过调用 .json({/*...*/}) 写入 response，因此它将 json“返回”给客户端。

一个简化的例子:

  setTimeout(() => {
    console.log("test");
  }, 1);

上面的代码向控制台输出一些内容，尽管箭头函数没有返回任何内容。