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# How to Find the Sum of an Array of Numbers with JavaScript?

Finding a sum of an array of numbers is something that we’ve to do a lot in our JavaScript apps.

In this article, we’ll look at how to find the sum of an array of numbers with JavaScript.

### Array.prototype.reduce

The JavaScript array’s reduce method lets us get numbers from an array and add them up easily.

To do this, we write:

const sum = [1, 2, 3, 4].reduce((a, b) => a + b, 0)
console.log(sum)

We call reduce with a callback to help us add up the numbers.

a is the accumulated result, which is the partial sum.

And b is the item that we’re iterating through.

In the 2nd argument, we pass in 0 to set the initial result of a .

Therefore, sum is 10.

### Lodash sum Method

Lodash has the sum method that is specially made to add up numbers in an array together.

For instance, we can write:

const array = [1, 2, 3, 4];
const sum = _.sum(array);
console.log(sum)

to call sum with the array number array.

### Loop

We can use a for-of loop to loop through an array of numbers and add them up.

For instance, we can write:

const array = [1, 2, 3, 4];
let sum = 0
for (const a of array) {
sum += a
}
console.log(sum)

We get number a from array and add them to sum .

Also, we can use a while loop to loop through the number array.

To do this, we write:

const array = [1, 2, 3, 4];
let sum = 0
let i = 0;
while (i < array.length) {
sum += array[i];
i++
}
console.log(sum)

### Array.prototype.forEach

We can also use the forEach method to loop through the number array and add up all the numbers.

For example, we can write:

const array = [1, 2, 3, 4];
let sum = 0
array.forEach(a => {
sum += a;
});
console.log(sum)

We call forEach with a callback.

Then in the callback, we get the value that’s being iterated through with the first parameter.

Then we add that value to the sum .

### Conclusion

There’re several ways we can use to find the sum of the numbers in a number array with JavaScript.

One way is to use the reduce method.

Other ways include using the for-of loop, while loop, or forEach to loop through an array.

## By John Au-Yeung

Web developer specializing in React, Vue, and front end development.