如何在forEach中使用箭头功能？

Question

I am studying about arrow function in Javascript.
I used forEach in two ways.
The one without arrow is working, but the one with arrow is not working.

Could you please let me know why?

    let ary = [1,2,3,4,5];

    function callback (i) {
        console.log(i);
    }

    // Working
    ary.forEach(callback);

    // Not working
    ary.forEach((i)=>callback);

Answer 1

In the "non-working" code, you're passing a function that returns a function ( callback ) to forEach. callback itself is never called.

This would actually call the function, but it is basically the same as directly passing callback directly to forEach as in your first example:

ary.forEach((i) => callback(i));

Please see the documentation for arrow functions .

Answer 2

you can use:

ary.forEach(i=>callback);

But you'd better use arrow function in this way,and there is no need to define function callback

 let ary = [1,2,3,4,5]; ary.forEach(i=>{ console.log(i); }); 

Arrow functions like anonymous functions. That's an array function,and i is the param.

i=>{
  console.log(i);
}

You can learn more from there Array Functions