TypeScript 2.x By Example

Type annotation

To specify a type to a variable or a function, TypeScript provides a syntax for defining a type preceded by a colon. Type annotation comes after the variable identifier. Types can be primitive types, or arrays, or complex types using classes and interfaces. The following example shows the basic syntax of defining types of variables and functions:

let num: number=42;function example(name: string, age:number): number{  return 42;}

In the first line, when defining a num variable, it's optional to assign a value as well. In the function example, we see that we can define the type of the input parameter, and also for the return value. This helps us in making sure that all function calls are maintaining the correct signature contract. ...