Uppercase & Lowercase- Sentence Case all letters – Javascript

Lowercase

var dog = "Hello World!";
var dog = dog.toLowerCase();
//dog now equals "hello world!"

Uppercase

var dog = "Hello World!";
dog = dog.toUpperCase();
//dog now equals “HELLO WORLD!”

Sentence Case
function capitaliseFirstLetter(string)
{
return string.charAt(0).toUpperCase() + string.slice(1);
}