Splitting last n digits of each value in the array in JavaScript

We have an array of numbers and need to extract the last n digits from each value. If a number has fewer than n digits, it remains unchanged.

const arr = [56768, 5465, 5467, 3, 878, 878, 34435, 78799];
console.log("Original array:", arr);

Original array: [ 56768, 5465, 5467, 3, 878, 878, 34435, 78799 ]

We need a function that takes an array and a number n, then returns the last n digits of each element. If an element has fewer than n digits, it stays the same.

Example with n = 2

For n = 2, we want the last 2 digits of each number:

const arr = [56768, 5465, 5467, 3, 878, 878, 34435, 78799];

const splitLast = (arr, num) => {
    return arr.map(el => {
        if (String(el).length 

Last 2 digits: [ 68, 65, 67, 3, 78, 78, 35, 99 ]


How It Works

The function converts each number to a string, checks its length, and extracts the last n characters using substr(). Finally, it converts back to a number.

// Step-by-step breakdown for 56768 with n=2
const number = 56768;
const str = String(number);           // "56768"
const length = str.length;            // 5
const lastTwoDigits = str.substr(length - 2, 2);  // "68"
const result = +lastTwoDigits;        // 68

console.log(`${number} ? ${result}`);


56768 ? 68


Alternative Using slice()

A cleaner approach using the modern slice() method:

const splitLastModern = (arr, num) => {
    return arr.map(el => {
        const str = String(el);
        if (str.length 

Using slice(): [ 768, 465, 467, 3, 878, 878, 435, 799 ]


Conclusion

Use String.slice(-n) to extract the last n digits from numbers. The function preserves numbers that are already shorter than n digits, making it reliable for mixed-length arrays.