Quiz: Predict the Output — Coercion

Test Your Type Coercion Intuition

Each question below involves JavaScript's type coercion rules. Don't just guess — trace the algorithm step by step using the Abstract Equality algorithm, ToPrimitive, ToNumber, and ToBoolean rules from the types and coercion lesson.

If you get fewer than 6 out of 8, revisit the coercion lesson. If you get all 8, you're in the top 1% of JavaScript developers on this topic.

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Question 1: The Classic

console.log([] + {});

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Question 2: Order Matters

console.log({} + []);

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Question 3: The Null Surprise

console.log(null == 0);
console.log(null > 0);
console.log(null >= 0);

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Question 4: Boolean Traps

console.log(true + true + true);
console.log(true == 1);
console.log(true === 1);

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Question 5: String Number Dance

console.log("5" - 3);
console.log("5" + 3);
console.log("5" - - "3");

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Question 6: Array Coercion Chain

console.log([1] == true);
console.log([0] == false);
console.log([""] == false);

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Question 7: The typeof Chain

console.log(typeof typeof 42);

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Question 8: The Grand Finale

console.log([] + [] + "foo".split(""));

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Scoring Guide