Capitalize the First Letter of a String in JavaScript

capitalizeFirstLetter.js

// Capitalize first letter
undefined = true;
((window,document,undefined) => {
const capitalize = word => {
    var upperCase = word.toUpperCase().substring(0,1)
    var lowerCase = word.toLowerCase().substring(1, word.length);
    
    return `${upperCase}${lowerCase}`;
}

// sample usage
console.log(capitalize("john")); // output John
console.log(capitalize("BRAVO")); // output Bravo
console.log(capitalize("BLAne")); // output Blane
})(window,document);