Reversing a string in JS.

strrev-copy.js

let str1 = "hello";
let str2 = "";

for (let i = str1.length - 1; i >= 0; i--) {
  str2 += str1[i];
}

console.log(str1, "=>", str2);

strrev-inplace-array.js

// Uses an array since JS strings are immutable
let arr = Array.from("hello");
let l = 0;
let r = arr.length - 1;

while (l < r) {
  const c = arr[l];
  arr[l++] = arr[r];
  arr[r--] = c;
}

console.log(arr.join(""));