JavaScript: Array.prototype.forEach

arrayX.forEach(f)

Apply function f to every element of the array arrayX. Return undefined. Original array is not changed.

The function f is passed 3 args:

1. current_element
2. current_index
3. arrayX.

const x1 = [1, 2, 3];

const ff = ((x) => {
  console.log(x);
});

x1.forEach(ff);

// prints
// 1
// 2
// 3

arrayX.forEach(f, thisArg)

Use thisArg for this Binding of f. If it is not given, undefined is used.

// example of using forEach with a second argument

function ff(n) {
  this["k" + n] = n; // add a property key kn with value of n, to thisBinding object
  return n + 1;
}

// new object
const obj = {};

// array
const arr = [1, 2, 3];

// apply ff to each arr, using obj as thisBinding of ff
arr.forEach(ff, obj);

// obj is changed
console.log(obj); // { k1: 1, k2: 2, k3: 3 }

forEach with break

If you need to exit forEach when a condition is met, use “every” or “some”.

• Array.prototype.every
• Array.prototype.some