What's Your IQ

QUESTION 1 / 15 · TYPES & COERCIONEasy

What does this log?

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

What this JavaScript test measures, in short

This test checks whether you can predict what real JavaScript does: how values convert, how equality works, where variables live, and in what order asynchronous code runs. It rewards knowing the language's rules over knowing a framework.

Every snippet behaves the same in any modern browser or in Node.js. The questions are our own and are not standardised against a population, so treat the result as a check on your knowledge, not a certification.

By What's Your IQ · Reviewed 4 Oct 2026

Format: 15 predict-the-output questions, 4 options each
Topics: Types and coercion, objects and arrays, scope and hoisting, async and the event loop
Standard: ECMAScript (ECMA-262), with a new edition every June since 2015
Language: Created by Brendan Eich at Netscape in 1995

QUESTION 14, STEP BY STEP

Why a promise beats a zero-second timer

JavaScript runs one thing at a time. Callbacks wait in two queues, and the promise queue (microtasks) is always emptied before the next timer (task) gets a turn. Step through it.

CALL STACK

log(1)

MICROTASKS

[object Object]

TASKS

[object Object]

CONSOLE

Synchronous code runs top to bottom. console.log(1) goes on the call stack and prints immediately.

OLD HABITS, MODERN FIXES

Most gotchas have a modern way out

OLDER STYLE

var total = 0;for (var i = 0; i < 3; i++) { total += i;}// i is still 3 out here

MODERN

let total = 0;for (let i = 0; i < 3; i++) { total += i;}// i doesn't exist out here

let and const are scoped to their block, can't be used before their line and, with const, can't be reassigned. That removes the traps in questions 10 to 13.

98%of websites use JavaScript in the browserAccording to W3Techs' ongoing survey of the most-visited sites, making it the most widely deployed programming language there is.¹

1995Ten days at Netscape. Brendan Eich wrote the first version, called Mocha, then LiveScript. It was renamed JavaScript for marketing reasons; it has little to do with Java.²

1997Standardised. Ecma International published the first edition of ECMA-262, the ECMAScript standard every browser engine now follows.³

2015The big update. ES2015 added let, const, arrow functions, classes, promises and modules, and fixed most of the traps in questions 10 to 13. Editions have been yearly since.³

2024 surveyStill the most used. About 62% of respondents to Stack Overflow's survey had used JavaScript in the past year, keeping it the most-used language in that survey for over a decade.⁴

W3Techs. Usage statistics of JavaScript as client-side programming language on websites.
Wirfs-Brock, A., & Eich, B. (2020). JavaScript: The first 20 years. Proceedings of the ACM on Programming Languages, 4(HOPL), 1–189.
Ecma International. ECMA-262: ECMAScript Language Specification.
Stack Overflow. (2024). 2024 Developer Survey: Technology.

Where to go next

TypeScript testTypeScript catches many of this page's coercion bugs before the code runs. Its test covers generics, narrowing and utility types.

Python testPython shares JavaScript's model of objects as shared references but is far stricter about types: "5" + 3 is an error there.

All programming testsTwelve languages and five frameworks, including React, Vue and Node.js, each with its own question set.

Read the code. Predict what JavaScript does.