Mark a parameter as optional with `?`.
Section: Functions and Parameters
Use optional parameters
typescript
typescript
function greet(name: string, prefix?: string) {
return `${prefix ?? "Hello"}, ${name}`;
}Explanation
Optional parameters become `T | undefined` in the body.
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Same sheet · prioritizing Functions and Parameters
Use default parameters
Provide a default value and keep a concrete type.
Declare function overloads
Expose multiple call signatures with one implementation.