Primitive Types & Annotations
Understand TypeScript primitive types and how to annotate variables.
Primitive Types & Annotations is a free TypeScript Academy lesson on CoddyKit. This is lesson 1 of 3. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the TypeScript Academy learning path, and your progress syncs across the web and the CoddyKit app. The TypeScript Academy course includes 3 lessons in total.
Intro to Primitives
Goal: Explore primitive types (string, number, boolean, null, undefined, bigint, symbol) and annotate variables clearly.
String & number
string and number are the most common primitive types. Use annotations for clarity when needed.
let title: string = "TypeScript";
let version: number = 5.4;
console.log(title, version);Boolean, null, undefined
boolean values are true/false. null and undefined represent absence; they have their own types.
let isDone: boolean = false;
let empty: null = null;
let notAssigned: undefined = undefined;
console.log(isDone, empty, notAssigned);bigint & symbol
bigint handles arbitrarily large integers. symbol creates unique identifiers, often for object keys.
let big: bigint =123456789012345678901234567890n;
let uniqueKey: symbol = Symbol("id");
nconsole.log(big, uniqueKey);Annotation syntax
Annotations come after the variable name with a colon. This makes code self-documenting.
let username: string = "Alice";
let age: number = 30;
let isMember: boolean = true;Inference vs annotation
Inference lets TS deduce types from values. Use explicit annotations for clarity, APIs, or when variables start empty.
Annotation check
Quick check: Which is the correct way to annotate a string variable?
Recap & next
Recap: TS supports multiple primitive types: string, number, boolean, null, undefined, bigint, symbol. Annotate with a colon after variable names.
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Frequently Asked Questions
Is the “Primitive Types & Annotations” lesson free?
Yes — the full text of “Primitive Types & Annotations” is free to read here on the web. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the TypeScript Academy course, upgrade to CoddyKit PRO. The TypeScript Academy course includes 3 lessons in total.
What will I learn in “Primitive Types & Annotations”?
Understand TypeScript primitive types and how to annotate variables. You practise TypeScript Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start TypeScript Academy?
No prior experience is required. TypeScript Academy on CoddyKit is structured for beginners through advanced learners, so you can start here or from the beginning and move at your own pace. This is lesson 1 of 3.
How long does the “Primitive Types & Annotations” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this TypeScript Academy lesson?
Yes. Every TypeScript Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Primitive Types & Annotations
- Type Inference & any vs unknown
- Union & Literal Types (basic narrowing intro)