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Unleashing the Power of TypeScript

Inferring Generics

Explore how TypeScript infers generic types to simplify your code while maintaining type safety. Understand creating and linking generic nodes in linked lists and using generics with classes to enforce consistent types across instances.

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TypeScript is always trying to get out of our way. If it can figure out what a generic ought to be, it will relieve us of the responsibility of telling it. Let’s take a look at the following code:

TypeScript 4.9.5
export const identity = <T>(x: T): T => {
  return x;
};
export const foo = identity<string>('foo');
export const two = identity(2);
console.log(foo);
console.log(two);

In the code above, we’re able to completely omit telling TypeScript what type T should be. It seems that we’re handing that function call a number, so it’s able to figure out that T is a number in this case.

We can also leverage this to simplify our linked list above:

TypeScript 4.9.5
type LinkedListNode<T> = {
  value: T;
  next?: LinkedListNode<T>;
};
const createLinkedListNode = <T>(value: T): LinkedListNode<T> => { 
    return { value };
};
const firstNode = createLinkedListNode('first');
const secondNode = createLinkedListNode('second');
firstNode.next = secondNode;
console.log(firstNode);

Let’s explain the code sample above:

  • Lines 6–8: We define a generic function named createLinkedListNode that receive a value as a parameter, and return the linked list node with that value.

  • ...