Annotate parameters and return values.

Section: Functions and Parameters

Type a function

typescript
typescript
function add(a: number, b: number): number {
  return a + b;
}
Explanation

Return annotations can improve clarity even when TypeScript can infer them.

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Related commands

Same sheet · prioritizing Functions and Parameters
Use optional parameters
Mark a parameter as optional with `?`.
OpenIn sheettypescriptsame section
Use default parameters
Provide a default value and keep a concrete type.
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Use rest parameters
Accept a variable number of arguments.
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Use a function type alias
Describe callback signatures explicitly.
OpenIn sheettypescriptsame section
Declare function overloads
Expose multiple call signatures with one implementation.
OpenIn sheettypescriptsame section
Narrow with `typeof`
Refine primitive unions using runtime checks.
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