Prove your JavaScript skills
JavaScript is easy to start and hard to master, which makes self-rated skill almost meaningless. Lemma records how you reason about the event loop, closures and async code in sessions and adaptive tests.
Preparing for an interview? JavaScript interview questions, junior to senior
What JavaScript competence looks like
Someone who really knows JavaScript can predict the order in which a mix of promises, timers and synchronous code will run. They know why a closure inside a loop captures the wrong value, what this points to in a callback, and when equality checks will surprise them. They read an unfamiliar stack trace calmly.
Day to day, that shows up as clean async code with proper error handling, modules that do one thing, and careful handling of mutation. They choose between arrays, maps and sets on purpose, avoid blocking the main thread, and know enough about the browser and Node runtimes to tell which one caused a bug.
Live debugging with a JavaScript practitioner
60 min · Learning · with Bruno H.
Bruno H. rated the session
Practitioner · after the call
Clear reasoning on the event loop. Talked through trade-offs first.
The event loop
Microtasks, macrotasks and rendering, and how they decide the order your code actually runs in.
Closures and scope
Lexical scope, captured variables, and using closures for encapsulation without leaking memory.
Async patterns
Promises, async and await, cancellation, and handling errors so failures never disappear silently.
Prototypes and this
How objects inherit, how classes map onto prototypes, and how call sites change the value of this.
Modules and tooling
ES modules, bundling, tree shaking and the difference between browser and Node module resolution.
Data structures
Choosing arrays, objects, maps and sets, plus non-mutating updates and safe copying of nested data.
What counts as evidence of JavaScript skills?
Listing JavaScript on a profile proves nothing on its own. What counts is a component you shipped, a session where someone watched you debug one, or a test you passed. These are the records Lemma can hold for your JavaScript skill, and where each one comes from. See the evidence methodology for how each source is weighed.
JavaScript
Jordan L. · SCI recomputed 9 Oct
Evidence · 4 entries
- Rated 5.0
Live debugging with a JavaScript practitioner
Live session · 9 Oct
- Level 7.2
Adaptive JavaScript assessment
Adaptive assessment · 2 Oct
- Verified
Commits that show your JavaScript
GitHub connector · 24 Sep
- Practice
Practice drills with the AI tutor
AI tutor practice · 11 Sep
Live debugging with a JavaScript practitioner
You trace a bug through real code while a practitioner watches your reasoning. Their rating of the session records how you handle async flow, scope and unexpected values.
Adaptive JavaScript assessment
Scenario questions on execution order, closures and coercion adjust to your level. Some show a snippet, and you choose the output it really logs or the cause of the bug.
Commits that show your JavaScript
Connect a repository or a single commit, such as a refactor or a tricky bug fix. Lemma confirms it exists and that you have access to it.
Practice drills with the AI tutor
Work through code exercises and explanations on weak spots like promise chaining. Drills add a small, capped amount to practice. They help you improve; they do not replace proof.
How is a JavaScript skills test run on Lemma?
The JavaScript test is adaptive: 15 to 25 questions, each picked from how you answered the last, built around real interface bugs rather than trivia. Its result joins your live sessions and linked repositories or deployments in your JavaScript SCI, which also weighs how recent the evidence is.
This logs 3, 3, 3. Why?
for (var i = 0; i < 3; i++) {
setTimeout(() => console.log(i));
}- AsetTimeout runs synchronously
- Bvar is function-scoped, so one i is shared
- CThe callbacks run before the loop
- Dconsole.log coerces i to a string
Debug real code in a session
Pair with a JavaScript practitioner on a bug or refactor. They watch how you read stack traces, reason about async timing and test your assumptions, then rate what they saw.
Pass the adaptive assessment
The test moves with you. Answer well and scenarios on the event loop, closures and prototypes get harder and count for more. Each question is timed, and you can't go back.
Connect and keep it fresh
Link GitHub work that shows idiomatic JavaScript. Keep booking sessions or practising, because evidence from long ago counts for less than recent work.
JavaScript skills: common questions
How can I test my JavaScript skills before applying for jobs?
What JavaScript concepts do senior engineers expect you to know?
Is knowing JavaScript enough, or should I learn TypeScript too?
How do I show JavaScript skills if my work code is private?
Skills related to JavaScript
Browse the skills directoryTypeScript
Show that your types catch real bugs instead of just silencing the compiler.
Evidence for TypeScriptReact
Show how you structure components, manage state and keep renders fast, with evidence behind it.
Evidence for ReactNode.js
Evidence of how you build and debug Node.js services, from the event loop to production errors.
Evidence for Node.jsVue.js
Show how you use reactivity, composables and component design in Vue, with evidence.
Evidence for Vue.js
Start your JavaScript evidence record.
Lemma is in early access. Request an invite and we will email you when your place is ready.