Level 1 exam — Node.js

Exam — fresh questions

12 questions to validate JavaScript & Node basics: modern JS, asynchrony, CommonJS/ESM modules and npm project management.
Answer everything, then click Check: your score and explanations will appear.

1.1 · Recall

1. Which reflex to adopt for declaring variables in modern JavaScript?

const by default, let if reassignment, never var var everywhere, as before let everywhere, never const No longer declare variables at all

const by default (stable reference, block scope), let if the value changes, var banned.

1.1 · Application

2. Salim wants the names of active users from a users array. Modern writing?

users.filter(u => u.actif).map(u => u.nom) A for loop with index and manual pushes Copy each name by hand into a new array Sort the array then take the first elements

filter keeps (the active ones), map transforms (their names): the intention reads at a glance.

1.1 · Arbitration

3. Salim re-reads const config = { port: 3000 } then config.port = 4000. Your call?

It's forbidden: const makes the object immutable, the code will crash The variable must be switched back to var to modify it It's valid: const prevents reassignment, not modifying the content The whole object must be recreated on each field change

const protects the “box” (the reference), not its content: changing a field stays possible.

1.2 · Recall

4. What does await do in an async function?

It turns the operation into classic synchronous code It ignores the operation's errors It waits for the result without blocking, code reads in order It blocks the whole program like a sleep

await suspends the function while waiting for the Promise without blocking the event loop.

1.2 · Application

5. Salim's console.log shows undefined just after an asynchronous call. Cause?

console.log doesn't work with files The read file is necessarily empty Node.js is broken, it must be reinstalled He reads the result too early: the operation isn't finished yet

Launching is not getting: the result arrives later (callback, .then() or await).

1.2 · Application

6. Salim chains three dependent operations (file → database → API). Recommended writing?

Three ordered awaits in an async function with try/catch Three blocking synchronous reads in series An arbitrary setTimeout between each operation Three nested callbacks in a pyramid

async/await: code reads in order, without blocking, errors handled in the same place.

1.3 · Application

7. Salim imports his local calculs.js module with CommonJS. Correct syntax?

require('calculs') with no ./ or extension import calculs from 'calculs' with no path Copy-paste the module's code at each use require('./calculs') with ./ for the local path

Local module = path with ./ or ../; bare name = native (fs) or npm package.

1.3 · Application

8. Salim starts a new project and wants the standard syntax (same as front-end). Choice?

Mix require and import in each file Enable ES Modules ("type": "module") and write with export/import Don't use modules at all Stay with CommonJS out of nostalgia for no reason

ESM = language standard, consistent front/back, recommended for a new project.

1.3 · Arbitration

9. Salim's project mixes require and import in the same file and crashes. Your call?

Rename files at random until it passes Choose one system per file per config and convert cleanly (explicit ESM extension) Drop modules and put everything back in one file Add even more mixing to compensate

One system per file: the config decides, don't mix without explaining it.

1.4 · Recall

10. What should be versioned in Git for a Node project?

node_modules only, the rest is useless The .env secrets to share them with the team Nothing at all, everything always regenerates Code + package.json + package-lock.json (never node_modules)

The recipe (json + lock) is versioned; node_modules regenerates via npm install.

1.4 · Application

11. Salim installs a restart tool only useful in development. Command?

Copy the tool by hand into node_modules npm install -D nodemon (devDependency, dev only) Add the tool to .gitignore instead of installing it npm install nodemon as a production dependency

-D marks dev packages: needed on the machine, not in production.

1.4 · Arbitration

12. Before releasing, npm audit reports a vulnerability in a dependency. Your call?

Release anyway, we'll see later Delete the lockfile to silence the alert Update the affected dependency, test, then release — never versioning .env Version node_modules to “freeze” the problem

Dependencies are a real attack vector: audit → update → test → release.

What's next?

Score ≥ 80%: move to Level 2 V3 (native fs/path/os modules, EventEmitter, streams and first HTTP server — Node's system building blocks).
Score between 50% and 80%: review the failed sections (modern JS 1.1, asynchrony 1.2, modules 1.3, npm 1.4), re-read the explanations above, then retake the test.
Score < 50%: restart the level from the beginning, running each snippet with node — asynchrony (1.2) deserves a full second read.