---
title: "Using type Annotations in Typescript Functions"
date: "2020-03-23"
slug: "using-type-annotations-in-typescript-functions"
author: "Dany Paredes"
canonical: "https://danywalls.com/using-type-annotations-in-typescript-functions"
description: "I am starting to move to Typescript. I discover how works type annotations in typescript functions. Let start by showing a few things I learned today about Typescript. Typescript allows type annotation in function parameters and returns types. Types ..."
---
I am starting to move to Typescript. I discover how works type annotations in typescript functions.
Let start by showing a few things I 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 style.
```javascript
function Authentication(user:string, age:Number) {
}
```
## Types in functions the return type
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.
```javascript
function isValid(user:string, age:Number) : boolean {
return true;
}
function removeCookies(user:string, age:Number) : void {
}
```
Another excellent Typescript features are the optional and default parameters.
## Optional parameter
Use optional parameters in functions are set adding a ? to the end of parameter declaration.
```javascript
function authentication(user:string, age?:Number, save) : boolean {
return true;
}
authentication("dany") //no compiler error.
```
## The default parameters value
If not passes the parameter to the function, it set a default value of 32 to it.
```js
function authentication(user:string, age:Number = 32, save) : boolean {
return age > 30
}
```
## Finish
Thanks for reading my small recap about using annotation types with Typescript in functions. If you enjoyed it, please share.
Photo by Max Delsid on Unsplash