javascript change case of a string lower to upper or upper to lower code example

Example 1: uppercase and lowercase letters in js

str.toLowerCase()
str.toUpperCase()

Example 2: how to find if given character in a string is uppercase or lowercase in javascript

var str = S;

  if (str == str.toUpperCase())
  {
    console.log(" Uppercase");
  }
  else
  {
    console.log("Lowercase");
  }