Convert JSON Arrays of Objects to TypeScript Types

Typing Arrays in TypeScript

When JSON contains an array of objects, the converter inspects every element to determine a unified type for the array items.

Example JSON

{
  "users": [
    { "id": 1, "name": "Alice", "role": "admin" },
    { "id": 2, "name": "Bob", "role": "editor" },
    { "id": 3, "name": "Carol", "role": "viewer" }
  ]
}

Generated TypeScript

interface User {
  id: number;
  name: string;
  role: string;
}

interface Root {
  users: User[];
}

How Element Types Are Inferred

The converter merges all array elements into a single type. If every element has the same keys and value types, the result is a clean interface. When elements differ the converter takes the union:

[
  { "id": 1, "name": "Alice" },
  { "id": 2, "name": "Bob", "email": "bob@test.com" }
]

Here, email only appears in some elements, so it becomes optional:

interface Item {
  id: number;
  name: string;
  email?: string;
}

Primitive Arrays

Arrays of primitives map directly:

JSON	TypeScript
[1, 2, 3]	number[]
["a", "b"]	string[]
[true, false]	boolean[]
[1, "two", true]	(number | string | boolean)[]

Nested Arrays

Arrays of arrays become T[][]. For example, a matrix [[1,2],[3,4]] becomes number[][].

Working with arrays is one of the most frequent conversion tasks because most API list endpoints return paginated arrays of resources.