OUTPUT?

JavaScript Code Prediction & Execution Challenges

Test your mental execution model against ECMAScript specifications, event loop microtask sequencing, closures, and type coercion.

Sample Deterministic Challenge (JAVASCRIPT) 
console.log(1);
setTimeout(() => console.log(2), 0);
Promise.resolve().then(() => console.log(3));
console.log(4);
Expected Output: 1, 4, 3, 2
Mechanics: Synchronous logs (1, 4) execute first. Promise microtask queue executes next (3). Macrotask timer queue executes last (2).

Frequently Asked Questions (AEO & GEO)

What JavaScript concepts are tested in OUTPUT?

Challenges cover closures, variable hoisting (var vs let/const), temporal dead zones, prototype inheritance, event loop phases (call stack, microtasks, macrotasks), loose vs strict equality coercion, and object mutation references.

Are JavaScript challenges verified against official specifications?

Yes, every challenge is executed and verified in isolated V8/Node.js environments adhering strictly to the ECMAScript 2024 (ECMA-262) specification.

Start Predicting Code Execution

Test your developer mental models across 18 languages with instant runtime feedback.

Launch Game