JavaScript

let/const vs var, block scope and hoisting - why old code behaves strangely and new code shouldn't.

Primitives vs objects, == vs ===, truthiness and the coercion rules interviewers love to probe.

Conditionals, loops, switch and early returns - plus the array methods that replace most loops.

Interpolation, common string methods and immutability - text handling you do every day.

Declarations vs expressions vs arrows, default and rest parameters - and how arrows change this.

Functions that remember their birthplace - the mechanism behind callbacks, privacy and most interview puzzles.

Functions that take and return functions - map/filter/reduce fluency and function composition.

Base cases and call stacks - for tree-shaped data and a class of interview questions.

Creation, destructuring, spread, optional chaining - the daily grammar of JS data.

The four binding rules (default, implicit, explicit, new) and how arrows opt out entirely.

The prototype chain as delegation - property lookup, class syntax and what instanceof really checks.

Beyond plain objects: keyed collections, iterables and for…of.

querySelector, creating and updating nodes, classList - the API frameworks wrap.

Bubbling, capturing, delegation and preventDefault - the model behind every interaction.

Reading values, validation and submission handling - the highest-stakes DOM work.

localStorage/sessionStorage, URL and History - platform features that remove dependencies.

Call stack, task queue and microtasks - why 'single-threaded' isn't the whole story, and what blocks it.

States, chaining, error propagation and combinators (all, race, allSettled).

Sequential-looking async code, try/catch error handling and parallelism pitfalls.

Requests with loading, error, retry and abort - the 80% of real-world async work.

class, constructors, inheritance, getters and private fields - the modern syntax over the prototype machinery you already understand.

Reachability, common leak patterns (forgotten listeners, growing caches) and what WeakMap is actually for.

Breakpoints, watch expressions, the performance panel and console beyond console.log - evidence over guesswork.

import/export, module scope and how bundlers stitch files into apps.

throw, custom errors and where to catch - failing loudly in dev, gracefully in prod.

package.json, semver and lockfiles - the contract of every JS project.

ESLint, Prettier and one Vitest test - automation that catches bugs before review.

Take the OneRoadmap JavaScript certification - 10 minutes to verified proof.