Skip to Content
Learning TypeScript 2.x - Second Edition
book

Learning TypeScript 2.x - Second Edition

by Remo H. Jansen
April 2018
Beginner content levelBeginner
536 pages
13h 21m
English
Packt Publishing
Content preview from Learning TypeScript 2.x - Second Edition

Union types

TypeScript allows you to declare union types:

let path: string[]|string;path = "/temp/log.xml";path = ["/temp/log.xml", "/temp/errors.xml"];path = 1; // Error

In the preceding example, we have declared a variable named path that can contain a single path (string) or a collection of paths (array of strings). In the example, we have also set the value of the variable. We assigned a string and an array of strings without errors; however, when we attempted to assign a numeric value, we got a compilation error, because the union type didn't declare a number as one of the valid types of the variable.

Union types are used to declare a variable that can store a value of two or more types. Only the properties available in all the types ...

Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.
Start your free trial

You might also like

Mastering TypeScript - Fourth Edition

Mastering TypeScript - Fourth Edition

Nathan Rozentals
Learning TypeScript

Learning TypeScript

Josh Goldberg
TypeScript for Beginners

TypeScript for Beginners

Bharath Thippireddy

Publisher Resources

ISBN: 9781788391474Supplemental Content