Using type Annotations in Typescript Functions.

#javascript #typescript #codenewbie

I am starting to move to Typescript. I discover how works type annotations in typescript functions.

Let start to show a few things learned today about typescript.

Typescript allows type annotation in function parameters and returns types.

Types in Function parameters.

The default type for the parameters in functions is any. Use : type after the declaration to set the type.

function Authentication(user:string, age:Number) {
}

The return type in functions allows set primitive, build-in types or custom types as a return type.

Use the void type for functions without a return value.

function isValid(user:string, age:Number) : boolean {
 return true;
}

function removeCookies(user:string, age:Number) : void {

}

Another nice Typescript features are the optional and default parameters.

The optional parameters can be set as optional adding a ? to the end of parameter declaration.

function authentication(user:string, age?:Number, save) : boolean {
return true;
}
authentication("dany") //no compiler error.

If the parameter is not passed it set a default value

function authentication(user:string, age:Number = 32, save) : boolean {
  return age > 30
}

This was a small recap about how to use annotation types with typescript in functions If you enjoyed please share.