JavaScript quick reference

The smallest Node.js program, and how console.log() prints.

const and let, numbers, strings, booleans, null / undefined, and converting between types.

if / else, switch, for, for…of, while, and the ternary operator.

Function declarations, arrow functions, default parameters, rest parameters and destructuring.

Arrays and their methods, sorting correctly, objects as records, and Map / Set.

Template literals, common string methods, splitting and joining, and regular expressions.

Wait for asynchronous work with async / await, run tasks together with Promise.all, and handle errors.

Read what you type in the IDE's Input tab: all at once with fs.readFileSync(0), or line by line.

Read project files with fs; write temporary files under /tmp.

Split a program into files with require / module.exports or import / export; no npm packages.

What Run does with your project, the time limit, input, tests, and what a run cannot do.

What ReferenceError, TypeError, SyntaxError and “Cannot find module” mean and how to fix them.

Where to read more: MDN for the language, the Node.js 22 docs for fs, process and other built-in modules.