Creating Self-Referencing Objects in TypeScript
Problem
Let’s consider a quick example: how would you create an object with the Node interface?
// define interface
interface Node {
value: number;
self: Node;
}
// create object
const node = {
value: 0,
self: ???,
};The problem is that you need a Node object reference for the self property. And to create the object you need to specify its self property. And so on, and so on.
Solution
The possible solution for this is to use a Partial mapped type. Here’s the code snippet for the solution:
function createNode(): Node {
const node: Partial<Node> = {
value: 0,
};
node.self = node as Node;
return node as Node;
}Partial<Node> returns a type that has got the same properties as Node, but those properties are optional. This allows to instanciate the object without specifying the self property right away. Once the object has been created, we can reference the object for the self property.
It’s important to cast the object from Partial<Node> back to Node before starting using it.