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Function Type Syntax

One of the most useful places for explicit types is in function signatures. For example:

function createMessage(name: string, a: number, b: number): string {
  return `${name} scored ${a + b}`;
}

The : type after each parameter specifies that parameter's type, and the : type after all the parameters specifies the return type. It works the same way with arrow functions:

const createMessage = (name: string, a: number, b: number): string => {
  return `${name} scored ${a + b}`;
};

Assignment

We need to calculate discounts for Support.ai customers. Run the function as-is, and notice that tsc is showing us some compile-time errors.

Fix the calculateTotal function by using the proper types. It should accept three parameters:

price: a number representing the base price
quantity: a number representing how many support chats they've purchased
discount: a number representing discount percentage (e.g., 0.1 for 10%)

Then return the total price (a number) after applying the discount.