Description

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Beginner · 10 min

Types and values

Use basic type annotations and distinguish type checking from execution.

Describe a value

TypeScript checks JavaScript before it runs. A type annotation describes an allowed value; it does not convert the value. This course assumes basic JavaScript knowledge.

const name: string = "Ada";
const tickets: number = 2;
console.log(name + ": " + tickets);

Output

Ada: 2

Types disappear at runtime

Annotations are removed when TypeScript becomes JavaScript. The playground checks your types before running the result. Runtime behavior still follows JavaScript rules.

const ready: boolean = true;
console.log(typeof ready);

Output

boolean

Put it into practice

  1. Read the types and predict the output before running the examples.
  2. Complete the task, then check your understanding with the practice questions.

Try it yourself

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Use a numeric value

Assign the number 4 to "count" and display it. Keep the number annotation.

Practice