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TypeScript: Documentation - More on Functions

typescriptlang.org · 5,844 words · saved by 1 readers

Functions are the basic building block of any application, whether they’re local functions, imported from another module, or methods on a class. They’re also values, and just like other values, TypeScript has many ways to describe how functions can be called. Let’s learn about how to write types that describe functions. The simplest way to describe a function is with a function type expression. These types are syntactically similar to arrow functions: The syntax (a: string) => void means “a function with one parameter, named a, of type string, that doesn’t have a return value”. Just like with function declarations, if a parameter type isn’t specified, it’s implicitly any. Note that the parameter name is required. The function type (string) => void means “a function with a parameter named string of type any“! Of course, we can use a type alias to name a function type: In JavaScript, functions can have properties in addition to being callable. However, the function type expression syntax

Functions are the basic building block of any application, whether they’re local functions, imported from another module, or methods on a class. They’re also values, and just like other values, TypeScript has many ways to describe how functions can be called. Let’s learn about how to write types that describe functions. Function Type Expressions The simplest way to describe a function is with a function type expression . These types are syntactically similar to arrow functions: ts function void): void' >greeter ( void' >fn : ( a : string ) => void ) { void' >fn ( "Hello, World" ); } function p

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