Javascript

Loops

for/of work with iterable objects

Introduced in ES6.

For/of with arrays, strings, sets

let data = [1, 2, 3, 4, 5], sum = 0;
for (let element of data) {
    sum += element
}

For/of with objects.

Objects are not by default iterable. Script below will throw an error:

let o = {x : 1, y: 2, z: 3}
for (let element of o) {
    console.log(element)
}

However we can use for/of to loop through object.keys(), object.values(), object.entries():

let pairs = "";
for (let [k, v] of Object.entries(o)) {
    pairs += k + v;
}

for/in

It has some tricky results. For example:

a is an array, i will be the index instead of the elements in a as expect.

for (let i in a) {
   console.log(i);
}