Null and Undefined

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This module will introduce you to Simple Types in TypeScript. You’ll learn about Arrays, Tuples, and Type Assertion, too.

Learning Objectives

The objectives of this module are to provide you with an understanding of:

  • What Simple Types are
  • How to use Arrays
  • How to use Tuples
  • How to use Type Assertion

Intended Audience

This learning path is aimed at all who wish to learn how to use TypeScript.


It is essential you understand the face of contemporary web development to attend this course. You should have a good working knowledge of Javascript. Please note: Before attending this class delegates must have a Microsoft account (signing up one is free).


We welcome all feedback and suggestions - please contact us at to let us know what you think.


The null and undefined primitive Javascript types are not very useful by themselves. I can assign null and undefined to other types such as number, string, any, and even void. If we compile this file, you can see that it compiles without any errors. However, TypeScript's compiler has a strict null checks flag, and this changes the behavior here. Observe what happens when we use the strict null checks flag. When added to the compiler you can see that we get some errors. We're not allowed to assign makeMeNumeric to null or undefined, but you are allowed to make the any type null or undefined. You can also see that the void type can only be assigned to undefined. It is recommended that this always be turned on, as it helps avoid many common errors. If you want to pass in a type with null or undefined as well, a union type could be used. Alternatively, set numerics to zero, strings to an empty string, objects to an empty object and so on, rather than null or undefined unless a specific need exists.


Simple Types: An Introduction - Arrays - Tuples - Any and Unknown - Function Arguments and Return Types - Enums - Type Assertion 

About the Author
Learning Paths

Ed is an Outstanding Trainer in Software Development, with a passion for technology and its uses and holding more than 10 years’ experience.

Previous roles have included being a Delivery Manager, Trainer, ICT teacher, and Head of Department. Ed continues to develop existing and new courses, primarily in web design using: PHP, JavaScript, HTML, CSS, SQL, and OOP (Java), Programming Foundations (Python), and DevOps (Git, CI/CD, etc). Ed describes himself as practically minded, a quick learner, and a problem solver who pays great attention to detail. 

Ed’s specialist area is training in Emerging Technologies, within Web Development. Ed mainly delivers courses in JavaScript covering vanilla JS, ES2015+, TypeScript, Angular, and React (the latter is authored by Ed) and has delivered on behalf of Google for PWAs. Ed has also developed a new suite of PHP courses and has extensive experience with HTML/CSS and MySQL. 

Ed is responsible for delivering QA’s Programming Foundations course using the Eclipse IDE. His skillset extends into the DevOps sphere, where he is able to deliver courses based around Agile/Scrum practices, version control, and CI/CD.

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