check if uppercase and lowercase of a letter are in a string javascript code example

Example 1: check if letter is uppercase javascript

isUpperCase('A') // true
isUpperCase('a') // false

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");
  }