Capitalize the first letter of the given word

Instructions:

Take the variable str and capitalize the first letter of the word. Put the result in a variable called newStr.

Expected result:

const str = 'javascript'
console.log(newStr); // Javascript

Solution:

const str = 'javascript';

// default value
let newStr = '';

if (str && isNaN(str)) {
  // If str is not empty, get the first char, capitalize and concatenate it with the rest of the string
  if (str.length > 0) {
    // if str has more than one char
    newStr = str.charAt(0).toUpperCase() + str.slice(1);
  } else {
    // if str has only one char
    newStr = str.toUpperCase();
  }
}

console.log(newStr);

Same solution using ES6 syntax:

const str = 'javascript';

let newStr = str && isNaN(str)
  ? str.length > 0
    ? str.charAt(0).toUpperCase() + str.slice(1)
    : str.toUpperCase()
  : '';

console.log(newStr);

Test Values:

str = 'javascript'; // Javascript
str = 'Javascript'; // Javascript
str = 'a'; // A
str = ''; // ''
str = null; // ''
str = undefined; // ''
str = 1234; // ''