Function types and default params

A parameter can have a default value - b: number = 2 means "if the caller leaves this out, use 2." That's real, runtime behavior (not erased like a type annotation): calling multiply(4) really does use b = 2.

You can also write a type for a function itself, when the function is stored in a variable or passed around: (a: number, b: number) => number describes "a function taking two numbers and returning one." Any function matching that shape - like multiply - can be assigned to a variable with that type.

Your task: write multiply(a, b) where b defaults to 2, then declare operation as a typed function variable pointing at multiply.

You'll practice:

Giving a parameter a default value
Writing a function-type annotation for a variable

// multiply(a, b): b should default to 2 when omitted.
function multiply(a: number, b: number = 2): number {

}

// Type operation as a function taking two numbers and returning a number.
const operation: (a: number, b: number) => number = multiply;

const doubled = operation(5);
const custom = operation(5, 3);