Basics of Typescript Built-in Types

Hello fellow Developers, recently I am learning Typescript and I want to share my knowledge and journey along the way.

Basic Typescript Types

  • Boolean
  • Number
  • String
  • Array
  • Enum
  • Void
  • Null
  • Undefined
  • Never
  • Any

Type Annotations

Type annotation is a way to describe a variable type while declaration.

let name: string = "Anna";
name = 12; //returns error

Even if you don’t annotate your variable, typescript infers your variable type on the base of the initial value.

let city = "Islamabad"; //city is type string here
city = 12; //returns error

And prevents you the assigning any value that doesn’t match with the initial value type.

Union Types

Typescript allows you to assign more than 1 type to a variable which will result in a union type.

const someVariable: string | number;
someVariable = "This is string"; //works perfectly
someVariable = 10; //works perfectly

Here someVariable can have a string value or a number value.

Type Assertions

Type assertions are used when you are getting dynamic value in your variable and then you need to perform some operation on it.

let fixedString: string = (<number>value).toFixed(4);

Here with <number> you are asserting the type of value variable as a number. In other words, you are telling your code value the variable should have a number type.
There is another way to do it

let fixedString: string = (value as number).toFixed(4);


In this blog, you learned about Typescript built-in types. How to Annotate and Assert variables in Typescript and last but not least How to create Union Types in Typescript.

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