Get the Index of the Max/Min value in Array in JavaScript

avatar
Borislav Hadzhiev

Last updated: Dec 21, 2022
5 min

banner

# Table of Contents

  1. Get the Index of the Max value in an Array
  2. Get the Index of the Min value in an Array

# Get the Index of the Max value in an Array in JavaScript

To get the index of the max value in an array:

  1. Use the Math.max() method to get the max value in the array.
  2. Use the String.indexOf() method to get the index of the max value.
  3. The indexOf() method returns the index of the value in the array or -1 if the value isn't found.
index.js
const arr = [3, 5, 8, 100, 20]; const max = Math.max(...arr); const index = arr.indexOf(max); console.log(index); // ๐Ÿ‘‰๏ธ 3

get index of max value in array

If you need to get the index of the min value, use the Math.min() function instead.

index.js
const arr = [10, 5, 0, 15, 30]; const min = Math.min(...arr); const index = arr.indexOf(min); console.log(index); // ๐Ÿ‘‰๏ธ 2

We used the Math.max() method to get the max value in the array.

The Math.max() method expects multiple, comma-separated numbers as arguments, so we can't just pass it an array directly.

index.js
const max = Math.max(3, 5, 8) console.log(max) // ๐Ÿ‘‰๏ธ 8

We used the spread operator (...) to unpack the values of the array and passed them as multiple, comma-separated arguments to the Math.max() method.

index.js
const arr = [3, 5, 8, 100, 20]; const max = Math.max(...arr); const index = arr.indexOf(max); console.log(index); // ๐Ÿ‘‰๏ธ 3

The last step is to use the Array.indexOf method to get the index of the max value.

If we had multiple array elements with the same max value, the indexOf method would return only the index of the first occurrence.

You can use a for loop to get the index of all max values in the array.

# Get the indexes of all elements with the max value in an array

To get the indexes of all elements with the max value in an array:

  1. Use the Math.max() method to get the max value in the array.
  2. Declare an indexes variable that stores an empty array.
  3. Iterate over the array and push only the indexes of the max values to the indexes array.
index.js
const arr = [3, 5, 8, 100, 20, 100]; const max = Math.max(...arr); const indexes = []; for (let index = 0; index < arr.length; index++) { if (arr[index] === max) { indexes.push(index); } } console.log(indexes) // ๐Ÿ‘‰๏ธ [3, 5]

get the indexes of all elements with the max value in array

We used a for loop to iterate for array.length iterations.

On each iteration, we check if the element at that index is the max value, and if it is, we push the current index to the indexes array.

The indexes array stores the index of all occurrences of the max value in the array.

You can also use the Array.reduce() method.

# Get the Index of the Max value in an Array using Array.reduce()

This is a three-step process:

  1. Use the Array.reduce() method to iterate over the array.
  2. Check if the current element is greater than the accumulator.
  3. If the condition is met, return the current index, otherwise, return the accumulator.
index.js
const arr = [3, 5, 8, 100, 20]; const index = arr.reduce((accumulator, current, index) => { return current > arr[accumulator] ? index : accumulator; }, 0); console.log(index); // ๐Ÿ‘‰๏ธ 3

get index of max value in array using reduce

The function we passed to the Array.reduce() method gets called with the accumulator value, the current array element and the current index.

The second argument we passed to Array.reduce() is used as the initial value for the accumulator variable.

We used 0 as the initial value.

Whatever we return from the function gets set as the new value of the accumulator variable.

On each iteration, we check if the current list item is greater than the element at the accumulator index.

If the condition is met, the current index is returned, otherwise, the accumulator index is returned.

After the last iteration, the index variable stores the index of the max value in the array.

# Get the Index of the Min value in an Array in JavaScript

To get the index of the min value in an array:

  1. Use the Math.min() method to get the min value in the array.
  2. Use the Array.indexOf() method to get the index of the min value.
  3. The indexOf method returns the index of the first occurrence of the value in the array.
index.js
const arr = [10, 5, 0, 15, 30]; const min = Math.min(...arr); const index = arr.indexOf(min); console.log(index); // ๐Ÿ‘‰๏ธ 2

We used the spread (...) operator when we called the Math.min() method.

The Math.min() method expects comma-separated numbers as arguments, so we can't directly pass it an array.
index.js
const min = Math.min(10, 5, 0) console.log(min) // ๐Ÿ‘‰๏ธ 0

We used the spread operator (...) to unpack the values of the array and passed them as multiple, comma-separated arguments to the Math.min() method.

We then used the Array.indexOf method to find the index of the first occurrence of the min value.

index.js
const arr = [10, 5, 0, 15, 30]; const min = Math.min(...arr); const index = arr.indexOf(min); console.log(index); // ๐Ÿ‘‰๏ธ 2
If there were multiple array elements with the value of 0, the indexOf method would return the index of the first occurrence.

If you need to find the index of all occurrences of the min value in the array, use a for loop.

index.js
const arr = [10, 5, 0, 15, 30, 0, 0]; const min = Math.min(...arr); console.log(min); // ๐Ÿ‘‰๏ธ 0 const indexes = []; for (let i = 0; i < arr.length; i++) { if (arr[i] === min) { indexes.push(i); } } console.log(indexes); // ๐Ÿ‘‰๏ธ [2, 5, 6]

We used the Mah.min() method to find the min value in the array and used a for loop to iterate over the array.

On each iteration, we check if the current array element is equal to the min value.

If the condition is met, we push the current index into the indexes array.

The indexes array stores the index of all occurrences of the min value in the array.

You can also use the Function.apply method as an alternative to the spread (...) operator.

# Get the Index of the Min value in an Array using Function.apply()

This is a three-step process:

  1. Use the Function.apply() method in the call to the Math.min() method.
  2. Use the Array.indexOf() method to get the index of the min value.
  3. The indexOf method returns the index of the first occurrence of the value in the array.
index.js
const arr = [10, 5, 0, 15, 30]; // ๐Ÿ‘‡๏ธ now using apply, instead of ... const min = Math.min.apply(null, arr); const index = arr.indexOf(min); console.log(index); // ๐Ÿ‘‰๏ธ 2

The only difference in the code is how we get the min value in the array.

The arguments we passed to the Function.apply() method are:

  1. The this argument - for our purposes it is irrelevant.
  2. The array whose values will be passed to the Math.min() method as multiple, comma-separated arguments.

Under the hood, the apply method unpacks the values of the array and passes them as multiple arguments to the function the method is called on.

# Additional Resources

You can learn more about the related topics by checking out the following tutorials:

I wrote a book in which I share everything I know about how to become a better, more efficient programmer.
book cover
You can use the search field on my Home Page to filter through all of my articles.

Copyright ยฉ 2024 Borislav Hadzhiev