# How to find the largest number in a JavaScript array

Let's learn how to find the largest number in a JavaScript array

Posted on July 09, 2021

There are two ways you can find the largest number from a JavaScript array:

• Using the `forEach()` array method
• Using the `reduce()` array method

This tutorial will help you learn how to do both. Let’s start with using the `forEach()` method first.

## Finding the largest number in an array using forEach()

The Array `forEach()` method allows you to loop over an array in order from the first index to the last index.

It accepts a `callback` function from which it passes the value contained inside the array for you to process.

``````Array.forEach(function callbackFn(element, index, array) {
// do something for each element
}, thisArg);
``````

Here’s an example of a `forEach()` method in action:

``````let arr = [4, 5, 6, 7, 8, 9, 10];

arr.forEach((element) => {
console.log(element);
});
``````

The code above should show the following logs:

``````4
5
6
7
8
9
10
``````

Knowing how the `forEach()` method works, Here’s how you can find the largest number in an array:

• Initialize a variable with the value `0` called `temp`
• Compare and see if the value of `temp` is smaller than the current element inside the loop
• If `temp` is smaller, then assign the current element value into `temp`

Here’s a working example of the steps above:

``````let arr = [4, 5, 6, 7, 8, 9, 10];
temp = 0;

arr.forEach((element) => {
if (temp < element) {
temp = element;
}
});

console.log(`The largest number in the array: \${temp}`);
``````

The resulting log will be as follows:

``````The largest number in the array: 10
``````

Let’s test the method by creating a randomized array of numbers:

``````let arr = [5, 2, 67, 37, 85, 19, 10];
temp = 0;

arr.forEach((element) => {
if (temp < element) {
temp = element;
}
});

console.log(`The largest number in the array: \${temp}`);
``````

The result of the code above will be 85

And that’s how you use the `forEach()` method to find the largest number in an array.

Let’s see how you can use the `reduce()` method to achieve the same goal next.

## Finding the largest number in an array using reduce()

The `reduce()` method allows you to execute a reducer function for each element in your array.

A reducer function takes the current accumulated value and the current value to produce a new value.

For example, suppose you have the following array:

``````let arr = [5, 2, 67, 37, 85, 19, 10];
``````

You can call the reduce method on the array as shown below:

``````arr.reduce(function (accumulatedValue, currentValue) {
// reducer function content
});
``````

The value you `return` from the function will be the `accumulatedValue` used for the next iteration of the `reduce()` method.

For the first iteration, the `accumulatedValue` will be assigned with the value at index zero. When the iteration is finished, the `reduce()` method will return a single value, which is the `accumulatedValue`.

Knowing this, you can call the `Math.max()` method inside the reducer function to compare the numbers between the `accumulatedValue` and the `currentValue`.

The returned value will be the largest number from the array as shown below:

``````let arr = [5, 2, 67, 37, 85, 19, 10];

let largestNum = arr.reduce(function (accumulatedValue, currentValue) {
return Math.max(accumulatedValue, currentValue);
});

console.log(`The largest number: \${largestNum}`);
// The largest number: 85
``````

And that’s how you find the largest number in an array using the `reduce()` method. You can learn more about the use of `reduce()` method here:

Understanding JavaScript reduce method

Related articles:

### Grab the free JavaScript book today 👍

Learn the building blocks of JavaScript programming language like data types, functions, objects, arrays and classes.

Use the knowledge from the book to build a small but solid program.