searchreplace.js

function myReplace(str, before, after) {
  let isCapitalized = w => w[0].toUpperCase() === w[0]
  let capitalize = w => w[0].toUpperCase() + w.slice(1)
  let lower = w => w[0].toLowerCase() + w.slice(1)  
  let r = []
  for(let w of str.split(" ")){
    if(w.toLowerCase() === before.toLowerCase()) {
      r.push(isCapitalized(w)?capitalize(after):lower(after))
    } else r.push(w)  
  }  
  return r.join(" ")
}