美元符号的JavaScript方法

var userName = "John Doe";
var userAge = 30;

function greetUser(name) {
    return "Hello, " + name + "!";
}

console.log(greetUser("John"));

var sum = 5 + 7;
var product = 8 * 5;

var person = {
    firstName: "John",
    lastName: "Doe",
    age: 30,
    getFullName: function() {
        return this.firstName + " " + this.lastName;
    }
};

console.log(person.getFullName());