JS: Set.prototype.forEach

(new in JS: ECMAScript 2015)

mySet.forEach(f)

• Apply function f to all values in set mySet.
• Does not modify the set object.
• Return undefined.

• f is passed 3 arguments, x y z.
• The x is the current value in the set, y is the same as x, z is the set being iterated.
• The reason the first two arguments are the same is because to keep compatible in form with the forEach method of Array.

const xx = new Set([3, 4, 5]);

// apply a function to each value
const yy = xx.forEach((x) => {
  console.log(x + 10);
  return x + 10;
});
/*
13
14
15
*/

// does not modify the variable
console.log(xx);
// Set(3) { 3, 4, 5 }

// returns undefined
console.log(yy);
// undefined

// 3 args form of f in forEach on a set object

const xx = new Set([3, 4, 5]);

// apply a function to each value
xx.forEach(function (aa, bb, cc) {
  console.log([aa, bb, cc]);
});

/*
[ 3, 3, Set(3) { 3, 4, 5 } ]
[ 4, 4, Set(3) { 3, 4, 5 } ]
[ 5, 5, Set(3) { 3, 4, 5 } ]
*/

mySet.forEach(f, thisArg)

Use thisArg for this (binding) of f. Default to undefined.