If you are at all familiar with JavaScript you will be very familiar with the concept of functions. TypeScript has added type annotations to the parameter list as well as the return type. Due to the new constraints being placed on the parameter list, the concept of function overloads was also included in the language specification. TypeScript also takes advantage of JavaScript's arguments object and provides syntax for rest parameters. Let's take a look at a function declaration in TypeScript:

function add(x: number, y: number): number {
    return x + y;
}

As you can see, we have created a function called add. It takes two parameters that are both of the type number, one of the primitive types, and it returns a number. This function is useful in its current form but it is a little limited in overall functionality. What if we want to add a third number to the first two? Then we have to call our function multiple times. TypeScript provides a way to provide optional parameters to functions...