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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

Generic constraints

Sometimes, we don't need the concrete type required by a function, class, or method, but we know that such type must adhere to a certain set of rules.

For example, the following code snippet declares a generic function named isEquals. However, this time the type T has a constraint (T extends Comparable):

interface Comparable<T> {    equals(value: T): boolean;}function isEqual<TVal, T extends Comparable<TVal>>(comparable: T, value: TVal) {    return comparable.equals(value);}

The constraint is used to ensure that all the types provided to isEqual as its generic type argument implement the Comparable interface:

interface RectangleInterface {    width: number;    height: number;}type ComparableRectangle = RectangleInterface & Comparable<RectangleInterface>; ...
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Publisher Resources

ISBN: 9781788391474Supplemental Content