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Solving TypeScript Errors

Solving TypeScript Errors

Type checking is awesome, but sometimes it gives you error messages that can be challenging to interpret and resolve.

Whether you're new to TypeScript or looking to deepen your understanding, this tutorial is your guide to understanding some of TypeScript's most common errors.

In this tutorial, you'll find challenges centered around reading error messages and practical solutions to solving the issues they describe. You'll gain insights into:

  • Type Not Assignable Error: Understand why type mismatches occur and explore solutions like widening type definitions.
  • Property Does Not Exist on Type Error: Learn how to deal with undeclared properties and the use of Record types.
  • Possibly Null or Undefined Error: Tackle nullability issues with techniques like optional chaining and type narrowing.
  • Types of Property are Incompatible Error: Decode complex error messages and refine your type definitions.
  • Type Unknown Error: Handle unknown types effectively.
  • Expression of Type String Can't Be Used to Index Type Error: Overcome indexing issues with strategic type refinements.
  • Property Has No Initializer and Is Not Definitely Assigned in Constructor Error: Address class property initialization challenges.
  • Conversion of Type May Be a Mistake Error: Navigate type conversion with caution.
  • Cannot Redeclare Block-scoped Variable Error: Resolve naming conflicts and understand TypeScript's module detection.
  • Could Not Find a Declaration File for Module Error: Deal with missing type declarations in JavaScript modules.


This tutorial is split into several exercises. Each features a problem that encourages you to take an active, exploratory approach to finding a solution.

You'll need to:

  • Watch and read the problem introduction.
  • Check out the TypeScript or React documentation or dive into type definitions to look for help
  • Try a solution and check your work. There may be more than one way to solve the challenge! Whether you succeed or get stuck, watch and read the solution and check out the included code.


You’ll need a working understanding of TypeScript.

Running the Exercises

Clone the Error Messages Tutorial repo, and use npm or yarn to install dependencies.

If you follow this link to use gitpod, you can work in a full VS Code coding environment running in your browser.

Follow the instructions in the README for more.


10 Lessons