Finding nth day of the year in leap and non-leap years in JavaScript

Problem

We are required to write a JavaScript function that takes in a number as the first argument and boolean as the second argument.

The boolean specifies a leap year (if it’s true). Based on this information our function should return the date that would fall on the nth day of the year.

Example

Following is the code −

const day = 60;
const isLeap = true;
const findDate = (day = 1, isLeap = false) => {
   if(day > 366){
      return undefined;
   };
   const months = ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'];
   const days = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
   if(isLeap){
      days[1]++;
   };
   let i = -1, count = 0;
   while(count < day){
      i++;
      count += days[i];
   };
   const upto = days.slice(0, i).reduce((acc, val) => acc + val);
   const month = months[i];
   const d = count - upto;
   return `${month}, ${d}`;
};
console.log(findDate(day, isLeap));

Output

Following is the console output −

Feb, 29