First Lesson was just a flash about TypeScript – today I will try to show you possible types and their valid and wrong values.

From specification:

TypeScript adds optional static types to JavaScript. Types are used to place static constraints on program entities such as functions, variables, and properties so that compilers and development tools can offer better verification and assistance during software development.

So we have this what in my opinion really miss in Javascript – strong typing!

In TypeScript types are categorized as primitive types, object types, union types, or type parameters;

Primitive types are:

• number
• boolean
• string
• any

• void
• null
• undefined

Let’s see possible values for this types

number

boolean

string

any

void

As we can see, we can’t assign string to number or number to bool etc – so we finally get it!

Interesting detail is that we can declare variable as void – but we can’t assign value. Void types are for function and methods – just for information that we shouldn’t expect any return value;
From documentation:

We might consider disallowing declaring variables of type Void as they serve no useful purpose. However, because Void is permitted as a type argument to a generic type or function it is not feasible to disallow Void properties or parameters.

For every primitive we can assign undefined or null.

For all primitive types we have mother – any (like Object in Java).

That’s why it’s possible to assign different types to variable with static constraint any.