JS foreach
last modified October 18, 2023
In this article we show how to create foreach loops in JavaScript.
C language popularized the classic for loop, where a counter is used to create a loop.
The foreach loop iterates over a collection of data one by one. In each loop, a temporary variable contains the current element.
JavaScript has forEach method and the for/of form to
loop over iterables.
JS forEach method
In the first example, we use the forEach method to go over the
elements of an array.
let words = ['pen', 'pencil', 'falcon', 'rock', 'sky', 'earth'];
words.forEach(e => console.log(e));
console.log("----------------------");
words.forEach((word, idx) => {
console.log(`${word} has index ${idx}`);
});
The example loops over elements of an array of words.
words.forEach(e => console.log(e));
In the first loop, we print all elements.
words.forEach((word, idx) => {
console.log(`${word} has index ${idx}`);
});
In the second loop, we print element with its index.
$ node foreach.js pen pencil falcon rock sky earth ---------------------- pen has index 0 pencil has index 1 falcon has index 2 rock has index 3 sky has index 4 earth has index 5
In the next example we use the forEach method to loop over a map.
let stones = new Map([[1, "garnet"], [2, "topaz"],
[3, "opal"], [4, "amethyst"]]);
stones.forEach((k, v) => {
console.log(`${k}: ${v}`);
});
We have a small map of stones. In each loop, the pair is destructured into a key and a value.
$ node foreach2.js garnet: 1 topaz: 2 opal: 3 amethyst: 4
JS for/of
The for/of statement iterates over a sequence of values from an iterable object.
let words = ['pen', 'pencil', 'falcon', 'rock', 'sky', 'earth'];
for (let word of words) {
console.log(word);
}
In the example, we go over the array of words using for/of statement.
In the next example we go over a map.
let stones = new Map([[1, "garnet"], [2, "topaz"],
[3, "opal"], [4, "amethyst"]]);
for (let e of stones) {
console.log(e);
}
console.log('------------------------');
for (let [k, v] of stones) {
console.log(`${k}: ${v}`);
}
We have two for/of loops.
for (let e of stones) {
console.log(e);
}
In the first loop, we go over elements.
for (let [k, v] of stones) {
console.log(`${k}: ${v}`);
}
In the second loop, we destructure each element into key and value items.
$ node for_of2.js [ 1, 'garnet' ] [ 2, 'topaz' ] [ 3, 'opal' ] [ 4, 'amethyst' ] ------------------------ 1: garnet 2: topaz 3: opal 4: amethyst
Source
In this article we have used foreach loops to go over elements of iterables in
JavaScript. We have utilized the forEach method and the
for/of statement.