danvk

const order = {
  what: 'Macbook Air' as Product, // or "as 'MacbookAir'"
  how: 'bitcoin'
};
purchase(order.what); // ok

danvk

const order = {
  what: 'Macbook Air',
  how: 'bitcoin'
};
order.what = 'Lenovo'; // valid

danvk

let newToy: Product = 'Macbook Air';
purchase(newToy); // ok

danvk

purchase('Macbook Air');
const newToy = 'Macbook Air';
purchase(newToy);  // ok

danvk

type Product = 'iPad' | 'Mac Mini' | 'Macbook Air' | 'Macbook Pro';
export function purchase(what: Product) {
 // mine bitcoin…
 // send to apple…
}

danvk

const loc: [number, number] = [10, 20];
panTo(loc);

danvk

const loc: any = [10, 20];
panTo(loc);
const loc = [10, 20];
panTo(loc as any);

danvk

const loc = [10, 20];
loc.push(30);

danvk

// Parameter is a (latitude, longitude) pair.
function panTo(where: [number, number]) { /* ... */ }

// Inline:
panTo([10, 20]);  // inline: ok

// Reference:
const loc = [10, 20];
panTo(loc);  // reference. Will this work?

danvk

export function purchase(what: string) { /* ... */ }

purchase('Macbook Air');  // Inline

const product = 'Macbook Air';
purchase(product);  // reference