为什么这个带有箭头功能的 IIFE 不执行？

Question

I'm curious why this IIFE will run

(function() {console.log("hi")}());  //"hi"

But with an arrow function it does not run

(()=> console.log("hi")());

why is this an error?

(()=> {return console.log("hi")}());

but moving the parenthase now it works

(()=> {return console.log("hi")})();//"hi"

The parenthese, and the function keyword are changing the behavior of the IIFE executing, anyone know why?

Answer 1

(()=> console.log("hi")());

An IIFE consists of a function definition, immediately followed by () .

An arrow function definition consists of some parameters, followed by => , followed by an expression.

console.log(...)() is an expression (meaning call console.log as a function, then call its return value as a function ), so it is treated as part of the function definition (and thus the () do not follow the function definition, because they are part of it).

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The parenthese, and the function keyword are changing the behavior of the IFFY executing, anyone know why?

They are a grouping operator . They surround the function definition making the () which follow it explicitly outside the function definition.