JuniorTheoryCommon

What does the program print?

TypeScript

function show(count: number | null) {
    if (count) {
        return "yes";
    }
    return "no";
}

console.log(show(0), show(-1));

no yes

Expecting if (count) to drop only null: a truthiness check drops every falsy value, and 0 is falsy, so show(0) returns "no".
Expecting tsc to reject a number in a condition: a condition need not be a boolean, so the zero bug shows up only at run time.

JuniorTheoryCommon

TypeScript

function show(count: number | null) {
    if (count) {
        return "yes";
    }
    return "no";
}

console.log(show(0), show(-1));

no yes

Expecting if (count) to drop only null: a truthiness check drops every falsy value, and 0 is falsy, so show(0) returns "no".
Expecting tsc to reject a number in a condition: a condition need not be a boolean, so the zero bug shows up only at run time.