My code does not work with forEach method

Question

I want to know why forEach would not work on this array but map does work.

I tried to use .map and it works but shouldn't forEach work as well

function letters() {
 let string = "abcd";
 let newString = string.split("").forEach(i => {
 return String.fromCharCode(i.charCodeAt(0) + 1);
 });
newString = newString.join("");
}

I get undefined when I use forEach

• Eric Guan: forEach and map do different things, they aren't interchangeable

Answer 1

shouldn't forEach work as well

No, it shouldn't. The documentation says:

Return value
undefined

This is the difference between map and forEach. They both call the function for each element of the array. map returns a new array containing the results, forEach ignores the results and doesn't return anything.

Answer 2

If you want to use forEach:

function letters() {
 let string = "abcd";
 let newString = '';
 string.split("").forEach(i => {
 newString += String.fromCharCode(i.charCodeAt(0) + 1);
 });
 return newString;
}