Run Length Encoding

run-length-encode.js

/**
 * Run Length Encoding
 * @author SourceBoy
 * @license MIT
 */

function runlengthEncode(input = '') {
  const chars = input.split('').concat([' ']);
  const out = []; 
  let [current] = chars;
  let i = 0;
  for (const c of chars) {
    if (c === current) {
      i++;
    } else {
      out.push(`${i}${current}`);
      i = 1;
    }   
    current = c;
  }
  return out.join('');
}