Typing objects in TypeScript

Typing objects in TypeScript

### Roles played by objects   In JavaScript, objects can play two roles (always at least one of them, sometimes mixtures): * Records: A fixed amount of properties that are known at development time. Each property can have a different type. * ...

Roles played by objects  

In JavaScript, objects can play two roles (always at least one of them, sometimes mixtures):

  • Records: A fixed amount of properties that are known at development time. Each property can have a different type.
  • Dictionaries: An arbitrary amount of properties whose names are not known at development time. All property keys (strings and/or symbols) have the same type, as do the property values.

First and foremost, we will explore objects as records. We will briefly encounter objects as dictionaries later in this post.

Types for objects  

There are two different general types for objects:

  • Object with an uppercase “O” is the type of all instances of class Object:
let obj1: Object;
  • object with a lowercase “o” is the type of all non-primitive values:
let obj2: object;

Objects can also be described via their properties:

// Object type literal
let obj3: {prop: boolean};

// Interface
interface ObjectType {
  prop: boolean;
}
let obj4: ObjectType;

In the next sections, we’ll examine all these ways of typing objects in more detail.

typescript

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