This the multi-page printable view of this section. Click here to print.

Return to the regular view of this page.

For..of loop

The for..of loop is for looping over objects that implement the Iterable interface (expose a Symbol.iterator property).

In this section we’ll demonstrate iterating over:

1 - Iterating over a string

const str = "hello";

for (const s of str) {
  console.log(s, typeof s);
}
  

h string
e string
l string
l string
o string

2 - Iterating over an array

const nums = [2, 3, 4];

let sum = 0;

// Use `let i` because i mutates (`i++`).
for (let i = 0; i < nums.length; i++) {
  sum += nums[i];
}

console.log(`sum: ${sum}`);
  

sum: 9

3 - Iterating over a set

const set = new Set([2, 2, 3, 3, 4, 4]);

for (const val of set) {
  console.log(val);
}
  

2
3
4

4 - Iterating over a map

Iterate over map entries as key,value tuples.

const map = new Map([
  ["a", 1],
  ["b", 2],
  ["c", 3],
]);

for (const entry of map) {
  console.log(entry);
}
  

[ "a", 1 ]
[ "b", 2 ]
[ "c", 3 ]

Iterate over the map, accessing the key and value parts as variables.

const map = new Map([["a", 1], ["b", 2], ["c", 3]]);

for (const [k, v] of map) {
  console.log(`key: ${k} => value: ${v}`);
}
  

key: a => value: 1
key: b => value: 2
key: c => value: 3

Iterate over just keys.

const map = new Map([["a", 1], ["b", 2], ["c", 3]]);

for (const [key] of map) {
  console.log(`key: ${key}`);
}
  

key: a
key: b
key: c

Iterate over just the values. Note that a placeholder is required for each key, as designated by the underscore (_).

const map = new Map([["a", 1], ["b", 2], ["c", 3]]);

for (const [_, value] of map) {
  console.log(`value: ${value}`);
}
  

value: 1
value: 2
value: 3