YDKJS 2: Getting started: Appendix B: Practicing Closure Problem Solution

closure.js

function range(start,end) {
    if(start == end) {
        return [start]
    }

    const printRange = (from, to) => {
      if(to === 0) {
        return [];
      }      
      return Array((to - from) + 1).fill(null).map((_, i) => start + i)
    }

    if(start < end) {
        return printRange(start, end)
    }

    if(typeof start === 'number' && end == undefined) {
        return function (end) {
            return printRange(start, end)
        }
    }
}

range(3,3);    // [3]
range(3,8);    // [3,4,5,6,7,8]
range(3,0);    // []

var start3 = range(3);
var start4 = range(4);

start3(3);     // [3]
start3(8);     // [3,4,5,6,7,8]
start3(0);     // []

start4(6);     // [4,5,6]