Generic Constraints

Constraints let a generic function require the members it needs.

constraints.ts

interface HasLength {
    length: number;
}

function lengthLabel<T extends HasLength>(value: T): string {
    return `length=${value.length}`;
}

const word: string = ;
const label: string = lengthLabel<string>(word);

console.log(label);

interface HasLength {
    length: number;
}

function lengthLabel<T extends HasLength>(value: T): string {
    return `length=${value.length}`;
}

const word: string = ;
const label: string = lengthLabel<string>(word);

console.log(label);

interface HasLength {
    length: number;
}

function lengthLabel<T extends HasLength>(value: T): string {
    return `length=${value.length}`;
}

const word: string = ;
const label: string = lengthLabel<string>(word);

console.log(label);

generic constraint A generic constraint such as `T extends HasLength` limits which values the generic function accepts.