Armstrong numbers between a range - JavaScript

A number is called Armstrong number if the following equation holds true for that number −

xy..z = x^n + y^n+.....+ z^n

Where, n denotes the number of digits in the number

For example − 370 is an Armstrong number because −

3^3 + 7^3 + 0^3 = 27 + 343 + 0 = 370

We are required to write a JavaScript function that takes in two numbers, a range, and returns all the numbers between them that are Armstrong numbers (including them, if they are Armstrong).

Example

Let’s write the code for this function −

const isArmstrong = number => {    let num = number;    const len = String(num).split("").length;    let res = 0;    while(num){       const last = num % 10;       res += Math.pow(last, len);       num = Math.floor(num / 10);    };    return res === number; }; const armstrongBetween = (lower, upper) => {    const res = [];    for(let i = lower; i <= upper; i++){       if(isArmstrong(i)){          res.push(i);       };    };    return res; }; console.log(armstrongBetween(1, 400));

Output

The output in the console: −

[    1,   2, 3, 4,   5,    6,   7, 8, 9, 153,    370, 371 ]