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$ curl repovive.com/roadmaps/javascript/introduction-to-typescript/generic-constraints

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$ curl repovive.com/roadmaps/javascript/introduction-to-typescript/generic-constraints

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Generic Constraints - Introduction to TypeScript | JavaScript | Repovive

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JavaScript22 sections · 783 units18h total

Open in Course

Generic Constraints

Limit what types are allowed

Constrain generic types with extends:

interface HasLength {
  length: number;
}

function logLength<T extends HasLength>(item: T) {
  console.log(item.length);
}

logLength("hello");  // OK: strings have length
logLength([1, 2]);   // OK: arrays have length
logLength(42);       // Error: numbers don't have length