Looping over all array entries is a common operation we do in JavaScript programs.
In this article, we’ll look at how to loop over all entries in a JavaScript array.
Array.prototype.forEach
We can use a JavaScript instance’s forEach method to loop through each entry of a JavaScript array.
For instance, we can write:
const a = ["a", "b", "c"];
a.forEach((entry) => {
console.log(entry);
});
We call forEach on a with a callback that gets the array entry from the first parameter.
Then we can do whatever we want with it in the callback.
for Loop
We can use a for loop to loop through all the items in a JavaScript array.
For instance, we can write:
const a = ["a", "b", "c"];
for (let index = 0; index < a.length; index++) {
console.log(a[index]);
}
We set index to 0, and we set the max loop limit to a.length .
And we increment index by 1 in each iteration with index++ .
Then in the loop body, we log a[index] to get the value of the a array entry with the given index .
Also, we can loop backward with:
const a = ["a", "b", "c"];
for (let index = a.length - 1; index >= 0; --index) {
console.log(a[index]);
}
We start with a.length , end the loop when index is 0, and we decrement index by 1 in each iteration.
The loop body is the same.
for-of Loop
Since ES6, we can use the for-of loop to loop through each array entry in our JavaScript code.
For instance, we can write:
const a = ["a", "b", "c"];
for (const val of a) {
console.log(val);
}
val has the value we’re iterating through.
a is the array.
The for-of loop works with any iterable object like maps and sets in addition to arrays.
Conclusion
We can loop through arrays with forEach , for loop, and for-of loop with JavaScript.
