Typing Constructor Values

What it is and why to use it

A construct signature describes a value that can be called with new. It is different from the instance type produced by that constructor. This is useful for passing a class into a small factory while checking the arguments and the shape of the created object.

Common mistakes and limitations

An interface describing instance methods does not automatically describe its constructor. Abstract constructors cannot be directly instantiated by a function like this; accepting them requires a different contract and an implementation that does not call new on an abstract type.

Run this example

Use TypeScript 5.8 or later with strict checking and an ES2022 target. Save each complete example independently as example.ts, compile it, then run the generated JavaScript with a compatible Node.js installation. Compiler-only options below affect checking; they do not add runtime validation.

Terminal — compile and run

npx tsc example.ts --strict --target ES2022 --module commonjs
node example.js

• constructor utility types
• classes basics

Syntax

type Factory = new (name: string) => Person;

Examples

class Person {
  constructor(public name: string) {}
}
function create(Type: new (name: string) => Person): Person {
  return new Type("John");
}
console.log(create(Person).name);

Best practices

• An interface describing instance methods does not automatically describe its constructor. Abstract constructors cannot be directly instantiated by a function like this; accepting them requires a different contract and an implementation that does not call new on an abstract type.
• Keep external-input validation separate from compile-time type descriptions.

Runtime & versions

Compiled to JavaScript. Feature availability depends on the language and runtime version used by your project; consult the official reference below.

Related TypeScript documentation

Specifications & further reading

• Official TypeScript documentation