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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

Conditional types

Conditional mapped types are an advanced feature introduced in TypeScript 2.8. Previously in this chapter, we learned that we could use the extends keyword to declare generic constraints. When we declare a generic constraint, we are using the extends keyword as a kind of operator that allows us to check if a generic type (T) is a subtype of a given type. For example, the following code snippet declares two interfaces named Animal and Dog:

interface Animal {    live(): void;}interface Dog extends Animal {    woof(): void;}

We then use the extends keyword as a conditional operator to generate a new type:

type Foo1 = Dog extends Animal ? number : string; // numbertype Bar1 = RegExp extends Dog ? number : string; // string

Conditional ...

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Publisher Resources

ISBN: 9781788391474Supplemental Content