JSFiddle - React, Tailwind, and code Playground

JavaScript

function foo(s) {
  for (let i = 0; i < s.length/2; i++) {
    if (i !== s.length-i-1) {
      s = s.substr(0,i).concat(
        s[s.length-i-1],
        s.slice(i+1, s.length-i-1),
        s[i],
        s.substring(s.length-i)
      )
    }
  }
  return s
}

console.log(foo('Leeroy Jenkins!!'))