CodingNeed.
TypeScript · Intermediate

TypeScript after JavaScript

Add types to familiar code and make function contracts clearer.

Prerequisite: JavaScript foundations · 59 minutes of guided study

6 published lessons, from first principles to a small project.

Open interactive course →

1 · Write contracts

  1. Describe a value

    Variables keep values available for later instructions.

    7 min →
  2. Type a function

    Functions turn inputs into outputs.

    8 min →
  3. Describe an object

    Objects group related properties.

    8 min →

2 · Model and build

  1. Narrow a union

    Arrays store values in order, starting at index zero.

    8 min →
  2. Keep a type relationship

    Arrays store values in order, starting at index zero.

    8 min →
  3. Project · Typed expense summary

    Combine loops, objects, conditions, and functions.

    20 min →