How could I write a for loop that adds up all the numbers in the array to a variable in JavaScript?

To sum all numbers in an array, initialize a total variable to 0, then iterate through the array and add each element to the total.

Let's say the following is our array with numbers:

var listOfValues = [10, 3, 4, 90, 34, 56, 23, 100, 200];

Using a for Loop

var listOfValues = [10, 3, 4, 90, 34, 56, 23, 100, 200];
var total = 0;

for (let index = 0; index < listOfValues.length; index++) {
    total = total + listOfValues[index];
}

console.log("Total Values = " + total);

Total Values = 520

Alternative Methods

You can also use other loop types or array methods:

var numbers = [10, 3, 4, 90, 34, 56, 23, 100, 200];

// Using for...of loop
let total1 = 0;
for (let num of numbers) {
    total1 += num;
}
console.log("Using for...of:", total1);

// Using reduce() method
let total2 = numbers.reduce((sum, num) => sum + num, 0);
console.log("Using reduce():", total2);

Using for...of: 520
Using reduce(): 520

Comparison

Conclusion

The traditional for loop provides full control and is perfect for learning. For cleaner code, consider using for...of or the reduce() method.