JuniorTheoryCommon

On which line does tsc report an error?

TypeScript

function longest<T extends { length: number }>(a: T, b: T): T {
    return a.length >= b.length ? a : b;
}

console.log(longest("cat", "horse"));
console.log(longest(10, 200));

Expecting the error in the declaration: the function is correct, and tsc reports the call whose argument breaks the constraint.
Expecting strings to fail because they are not objects: a constraint asks only for the properties, and every string has length.

Why does a.length compile inside longest, while a.toUpperCase() would not?
What does longest([1, 2], [3]) return, and what is its type?

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Back to questions

JuniorTheoryCommon

On which line does tsc report an error?

TypeScript

function longest<T extends { length: number }>(a: T, b: T): T {
    return a.length >= b.length ? a : b;
}

console.log(longest("cat", "horse"));
console.log(longest(10, 200));

Expecting the error in the declaration: the function is correct, and tsc reports the call whose argument breaks the constraint.
Expecting strings to fail because they are not objects: a constraint asks only for the properties, and every string has length.

Why does a.length compile inside longest, while a.toUpperCase() would not?
What does longest([1, 2], [3]) return, and what is its type?

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