javascript - Why can't forEach in es6 be written like this??

Question

map and forEach, why the third one is invalid

    let arr0=[1,2,3,5,0,9,1000,294,85,3850];
    
    console.log(arr0.map(x=>x+x));
    arr0.map(x=>console.log(x+x));

    console.log(arr0.forEach(x=>x+x)); // ??
    arr0.forEach(x=>console.log(x+x));

How to output the value of forEach as an array??

Answer 1

Okay, actually x=>x+x is an abbreviation, which is equivalent to x=>{return x+x;}; return in forEach will terminate the traversal

Answer 2

forEach的返回值是undefined

Answer 3

forEach has no return value and needs to be written in two steps, or use the last method

Answer 4

If you want this effect, you need to manually create a new array and operate it in forEach

var resultArr = []
arr.forEach((item) => {resultArr.push(item)})
console.log(resultArr)

Answer 5

As the name suggests, for each means "for each operation", and map means "one-to-one matching".

So forEach will not care about the return value.

It’s pointless to ask why something like this is artificially set, check the API more.