TypeScript Explained


Type is an alias that describe type of an object or property in TypeScript.

type Color = 'red';

Types cannot be extended, merged or implemented from. They can describe all kind of types including primitives (undefined,null, boolean, string or number) as well as union or intersection types. 1

They can be used in computed properties - it means that iterating through union keys is possible 1:

type Color = 'red' | 'blue';

type Computed = {
  [color in Colors]: string;

You can use type in conditional types:

type Num = 'number';
type Str = 'string';

type TypeOfValue<T> = T extends string ? Str : Num;

type value = TypeOfValue<'42'>; // 'string'
type value2 = TypeOfValue<42>; // 'number'
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