String.prototype.charAt()

= > Get first character of string using charAt[0] method.

String.prototype.toUpperCase()

=> Use toUpperCase() to capitalize first letter of string that is returned by charAt method 

'somestring'.charAt(0).toUpperCase() + 'somestring'.slice(1)

Here is the simple function that you can use multiple times

function capitalize(string) {
    return string.charAt(0).toUpperCase() + string.slice(1).toLowerCase();
}