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TypeScript fundamentals

TypeScript fundamentals is a free, beginner online course from Herizon.

Add types to the JavaScript you already know. Set up the TypeScript compiler, type functions, objects and lists, handle missing values, check data from an API and read the type errors a team will show you.

You finish with TypeScript added to your Herizon profile.

Free · 40 min read · certificate when you pass the quiz · part of Technical founder · last updated 12 November 2026

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Free account, about two minutes. You can join if you live in the EU, EEA, UK or Switzerland, or a partner organisation invited you.

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A look inside the course

  • Step 1: A booking card for a city bike, one day, with a helmet, showing 155 euros crossed out and 20 euros next to it
  • Step 2: A bookings.ts file goes through the tsc check and comes out as plain JavaScript with the types removed
  • Step 3: An editor line with a red underline under the text "15", where a number is expected
How page 1 starts: Why TypeScript: the 155 euro booking

Yasmin is a junior frontend developer at Kaarna Bikes, a made-up bike rental in Turku. Her first task is to move the booking code from JavaScript to TypeScript, because a customer saw a wrong price on the site.

It takes about 40 min of reading, plus exercises, a short quiz and a practice task. It teaches TypeScript. Pass the short quiz at the end to get a certificate.

What you will be able to do

  • A project where npx tsc checks your code with strict on
  • Typed functions, objects, lists and union types
  • A way to handle a value that may be missing
  • A check for data that comes from an API
  • The skill to read the type errors a team will show you
Start this course free

Who it is for

Time per page: about half an hour Whole course: a few hours with the practice project (11 pages, at your own speed) This is for you if you are: - A web developer who knows JavaScript and wants to learn TypeScript - Aiming at a frontend or full-stack role - A student who has seen .ts files in a project and wants to understand them You need a laptop where you can install Node.js and a code editor. You need to know basic JavaScript: variables, functions and objects. The course Web development fundamentals teaches it. ---

The situation you work through

Yasmin, a junior frontend developer at Kaarna Bikes, a made-up bike rental in Turku, moves the site's booking code from JavaScript to TypeScript after a one-day city bike with a 5 euro helmet showed 155 euros instead of 20, then types the three bikes (city 15, e-bike 35, cargo 45 euros a day), handles a bike that is not found and checks the bike list that comes from the API.

Your practice task

Move one small JavaScript file to TypeScript with strict on: your own code or the bookings.js starter on the last page. Use the course tsconfig and run npx tsc until it reports no errors. Type every function's parameters and return value, add one interface and one union type, guard one lookup that can come back undefined, and read one piece of JSON as unknown and check it before use. No any and no as without a comment that says why. Submit the .ts file, your tsconfig.json, and the first three compiler errors you met with one sentence each on how you fixed it.

Key topics

  1. Why TypeScript: the 155 euro booking
  2. Set up TypeScript and run your first check
  3. Basic types and inference
  4. Typing functions
  5. Objects and interfaces
  6. Lists and union types

and 5 more pages

What you get when you pass

A certificate with your name, the course and the date. Sharing it is your choice. If you share it, it has a public link that anyone can open to check it, and you can add it to LinkedIn.

Common questions about TypeScript fundamentals

Is TypeScript fundamentals free?
Yes. The course is free with a Herizon account, and the account is free too.
How long does TypeScript fundamentals take?
It takes about 40 min of reading, plus exercises, a short quiz and a practice task. You can stop and continue later, because the portal keeps your place.
Do I get a certificate?
Yes. Pass the short quiz at the end to get a certificate you can share, for example on LinkedIn.
What do I need to start?
A free Herizon account. The course is written at beginner level.
Who can join Herizon?
You can join if you live in the EU, EEA, UK or Switzerland, or a partner organisation invited you.
Who is TypeScript fundamentals for?
Time per page: about half an hour Whole course: a few hours with the practice project (11 pages, at your own speed) This is for you if you are: - A web developer who knows JavaScript and wants to learn TypeScript - Aiming at a frontend or full-stack role - A student who has seen .ts files in a project and wants to understand them You need a laptop where you can install Node.js and a code editor. You need to know basic JavaScript: variables, functions and objects. The course Web development fundamentals teaches it. ---

Start TypeScript fundamentals free

Start this course free

Common questions about TypeScript fundamentals

Is TypeScript fundamentals free?
Yes. The course is free with a Herizon account, and the account is free too.
How long does TypeScript fundamentals take?
It takes about 40 min of reading, plus exercises, a short quiz and a practice task. You can stop and continue later, because the portal keeps your place.
Do I get a certificate?
Yes. Pass the short quiz at the end to get a certificate you can share, for example on LinkedIn.
What do I need to start?
A free Herizon account. The course is written at beginner level.
Who can join Herizon?
You can join if you live in the EU, EEA, UK or Switzerland, or a partner organisation invited you.
Who is TypeScript fundamentals for?
Time per page: about half an hour Whole course: a few hours with the practice project (11 pages, at your own speed) This is for you if you are: - A web developer who knows JavaScript and wants to learn TypeScript - Aiming at a frontend or full-stack role - A student who has seen .ts files in a project and wants to understand them You need a laptop where you can install Node.js and a code editor. You need to know basic JavaScript: variables, functions and objects. The course Web development fundamentals teaches it. ---

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