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Functions: Call Signatures & Overloads
6 exercises
Functions are the heart of TypeScript programs. You can describe a function's shape with a call signature:
type MathOperation = (a: number, b: number) => number;
const add: MathOperation = (a, b) => a + b;Function overloads let one function name support different input shapes with different return types:
function parse(input: string): string[];
function parse(input: number): number[];
function parse(input: string | number) {
// Implementation handles both cases
}You write multiple signatures (overloads), then one implementation that handles all cases. The compiler picks the right signature based on what you pass in.
In this category, you'll:
- Write function type expressions (
type Fn = (x: number) => string) - Use optional parameters (
name?: string) and rest parameters (...args: number[]) - Create overloaded functions that return the correct type based on inputs
- Understand when to use overloads vs. union types
Best practice: Keep each branch simple and predictable. The focus is on readable types with small, safe implementations.