{} 作为箭头 JavaScript IIFE 的 function 版本的解释是什么？

Question

The normal arrow function version of an IIFE is this:

(() => {
  console.log('IIFE 1');
})();

But I've found here that also the following (really short) form works:

As a bit of extra credit there's an even shorter way to write IIFEs in ES6 which is to use the new function context syntax all on its own like so:

{
  console.log('IIFE 2');
}

Why only {} is enought?

Answer 1

The first example creates a function (which calls console.log ), then immediately calls it.

The second example doesn't create a function. It just has a block .

Answer 2

Well what's the point of calling an IIFE? it's to run some code in it's own context, right?

Thats what curly brackets do, they group blocks of code. From ES6, variables declared with const or let are not available from outside a block of code. So

(() => {
  var x = 'IIFE 1'
  console.log(x);
})();

and

{
  let x = 'IIFE 1'
  console.log(x);
}

are equivalent

Answer 3

Because it satisfies both conditions required by an IIFE (Immediately Invoked Function Expression):

• To prevent external access to the variables within the IIFE, as well as avoid polluting the global scope.
• It is executed immediately.

https://developer.mozilla.org/en-US/docs/Glossary/IIFE

The only limitation, as the author indicates, is that you can't pass external parameters to the block.