Tutorials/JavaScript

JavaScript tutorial

Add behavior to the web and build applications.

45 lessonsExamples and guided walkthroughs

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Course contents

Programming fundamentals

JavaScript Variables

Use const and let for values.

JavaScript Functions

Write reusable logic.

JavaScript conditions and array loops

Filter values with strict comparisons and accumulate a total.

JavaScript map, filter, and reduce

Build a transformation pipeline without mutating the source.

JavaScript types, equality, and coercion

Know the primitive types, why === is safer than ==, and which values count as false.

JavaScript closures and scope

Use a function that remembers its surrounding variables, and see why let fixes the classic loop bug.

JavaScript destructuring, spread, and rest

Unpack objects and arrays into variables, copy with spread, and collect arguments with rest.

JavaScript string methods and regular expressions

Split, pad, replace, and extract parts of text with strings and regular expressions.

JavaScript promises, async, and await

Write asynchronous code that reads like synchronous code, and handle errors with try and catch.

Object-oriented programming

JavaScript classes and private fields

Protect instance state with a private class field.

JavaScript inheritance and overriding

Reuse initialization and specialize instance behavior.

JavaScript prototypes and class inheritance

See that classes are built on prototype chains, and extend one constructor from another.

JavaScript private fields, getters, and static members

Hide state with #private fields, expose it through a getter, and keep a counter on the class itself.

Data structures and algorithms

JavaScript binary search

Search a sorted numeric array with a shrinking interval.

JavaScript Map and Set

Count values and identify distinct entries.

JavaScript linked lists and iterators

Build a singly linked list class that can be looped over with for...of.

JavaScript stacks and queues

Use an array as a stack, and write a queue that does not shift the whole array on every removal.

JavaScript sorting and the default sort pitfall

Learn why [10, 9, 1].sort() is wrong, sort with comparators, and write a merge sort.

JavaScript binary search trees with a generator

Insert values, search, and produce the sorted order lazily with a recursive generator.

JavaScript graphs: BFS, DFS, and path existence

Store a graph as a Map of neighbour lists and search it breadth-first and depth-first.

Analysis of algorithms

JavaScript: memoization trades memory for time

Count the calls made by a naive recursive Fibonacci and a memoized one.

JavaScript: counting the steps of binary search

Show that searching a sorted array of 1000 items takes at most about ten comparisons.

Database systems

JavaScript: an index turns a scan into a lookup

Compare scanning an array for a row with looking it up in a Map keyed by id.

JavaScript: GROUP BY and HAVING with Map

Total a column per group, keep the groups that pass a condition, and sort them.

Operating systems

JavaScript: the event loop as a cooperative scheduler

Predict the order in which synchronous code, nextTick, promises, and timers run in Node.js.

JavaScript: LRU replacement with a Map

Use Map's insertion order to evict the least recently used page and count page faults.

Computer networks

JavaScript: an HTTP server and client on the loopback interface

Start a Node.js HTTP server on a free port and request it with fetch to see status codes.

JavaScript: a TCP echo server with the net module

Send a line through a TCP socket and print the server's reply.

Software engineering

JavaScript: unit tests with node:assert

Write small tests with assertions, including checks that bad input throws the right error.

JavaScript: the observer pattern with EventEmitter

Let several listeners react to the same event without the emitter knowing about them.

Information security

JavaScript: SHA-256 hashing and HMAC with node:crypto

Hash a message, authenticate it with a secret key, and compare tags in constant time.

JavaScript: storing passwords with scrypt and a salt

Derive a memory-hard hash from a password and a random salt, then verify a login attempt.

JavaScript: preventing XSS by escaping output

Turn special HTML characters into entities so user text is shown as text, never run as markup.

Parallel and distributed computing

JavaScript: concurrency without parallelism

See how async functions interleave on a single thread and finish together under Promise.all.

JavaScript: real parallelism with worker threads

Split an array between two worker threads and add their partial results.

Artificial intelligence

JavaScript: breadth-first search for the fewest steps

Find a shortest path in an unweighted graph by exploring it layer by layer.

JavaScript: constraint satisfaction by backtracking

Color a map so that neighbouring regions differ, counting every valid coloring.

Knowledge representation and reasoning

JavaScript: querying facts stored as triples

Represent knowledge as subject–predicate–object triples and answer queries with variables.

JavaScript: proof by resolution refutation

Show that a knowledge base entails a query by deriving a contradiction from the knowledge base plus the negated query.

Machine learning

JavaScript: fitting a line with least squares

Compute the slope, intercept, and R² of the best-fit line in closed form.

JavaScript: a naive Bayes text classifier

Classify short messages as spam or ham from word counts with Laplace smoothing.

Neural networks and deep learning

JavaScript: a forward pass through two dense layers

Multiply by weight matrices, add biases, apply ReLU, and finish with softmax probabilities.

JavaScript: checking a gradient numerically

Compare a hand-derived gradient with a finite-difference estimate, the standard test for backpropagation code.

Computer vision

JavaScript: RGBA pixel arrays and Uint8ClampedArray

Convert pixels stored the way a canvas stores them to grayscale and see how clamping works.

JavaScript: a sharpen filter and why clamping matters

Apply a sharpening kernel to a step edge and see the overshoot clamped to the valid range.