JuniorTheoryCommon

Which type does TypeScript infer for `popped`?

TypeScript

class Stack<T> {
    private items: T[] = [];
    push(item: T): void {
        this.items.push(item);
    }
    pop(): T | undefined {
        return this.items.pop();
    }
}
const s = new Stack<string>();
s.push("a");
const popped = s.pop();

string | undefined

Expecting plain string because one item was pushed: tsc does not count pushes, and pop() is declared to return T | undefined.
Expecting T in the result: the type argument string fills T everywhere in the object s, in push and pop alike.

What does tsc report for s.push(5)?
What type does new Stack() get without a type argument, and why?

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Back to questions

JuniorTheoryCommon

Which type does TypeScript infer for `popped`?

TypeScript

class Stack<T> {
    private items: T[] = [];
    push(item: T): void {
        this.items.push(item);
    }
    pop(): T | undefined {
        return this.items.pop();
    }
}
const s = new Stack<string>();
s.push("a");
const popped = s.pop();

string | undefined

Expecting plain string because one item was pushed: tsc does not count pushes, and pop() is declared to return T | undefined.
Expecting T in the result: the type argument string fills T everywhere in the object s, in push and pop alike.

What does tsc report for s.push(5)?
What type does new Stack() get without a type argument, and why?

Back to questions Open topic in roadmap →Answer it yourself — Quiz

Which type does TypeScript infer for popped?

Which type does TypeScript infer for popped?

Which type does TypeScript infer for `popped`?

Which type does TypeScript infer for `popped`?