Counting number of 9s encountered while counting up to n in JavaScript

Problem

We are required to write a JavaScript function that takes in a number n. Our function should count and return the number of times we will have to use 9 while counting from 0 to n.

Example

Following is the code −

 Live Demo

const num = 100; const countNine = (num = 0) => {    const countChar = (str = '', char = '') => {       return str       .split('')       .reduce((acc, val) => {          if(val === char){             acc++;          };          return acc;       }, 0);    };    let count = 0;    for(let i = 0; i <= num; i++){       count += countChar(String(i), '9');    };    return count; }; console.log(countNine(num));

Output

Following is the console output −

20