TypeScript Optional

Örnek

Şöyle yaparız

interface Cat {
  name: string;
  age: number;
  ownerName?: string; // not every cat has an owner
}

const mrWhitePaws: Cat = {
  name: "Mr. White Paws",
  age: 7,
  ownerName: "Jane", // domestic cat, lucky guy
};

const wildLynx: Cat = {
  name: "Lynx lynx",
  age: 6,
  // this wild cat lives a free life!
};

Örnek

null Guard yerine Optional kullanmak çok daha kolay. Şöyle yaparız.

element?.innerText = 'Hello';

optional chaining ve nullish coalescing

Açıklaması şöyle

The optional chaining allows to safely “navigate” through possibly absent values (without throwing an error), while the nullish coalescing operator, or the ??, enables providing a failover (default) value in case of stumbling upon a null (think of it as a good, old || operator, but for null or undefined values only, instead of all “falsy” ones). Again, keep in mind, that this is an example of a feature eventually available in pure JavaScript, too.

Örnek

Şöyle yaparız

// optional chaining:
// The value will be undefined. Without `?.`, this would error with
// "Uncaught TypeError: Cannot read property 'length' 
const nameLength: string | undefined = wildLynx?.name?.length; of undefined".

// nullish coalescing:
const nope = null;
const calculation = (nope ?? 0) + 42; // The value will be 0 + 42, ergo 42.