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Exercise 9

Without running this code, what will it print?

console.log(false ?? null);
console.log(true ?? (1 + 2));
console.log((1 + 2) ?? true);
console.log(null ?? false);
console.log(undefined ?? (1 + 2));
console.log((1 + 2) ?? null);
console.log(null ?? undefined);
console.log(undefined ?? null);

Solution

console.log(false ?? null);         // => false
console.log(true ?? (1 + 2));       // => true
console.log((1 + 2) ?? true);       // => 3
console.log(null ?? false);         // => false
console.log(undefined ?? (1 + 2));  // => 3
console.log((1 + 2) ?? null);       // => 3
console.log(null ?? undefined);     // => undefined
console.log(undefined ?? null);     // => null

Remember that ?? returns the second operand if the first operand is either null or undefined. In all other situations, it returns the first operand.

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