Array Destructure

array-destructure.ts

// a 'Person' object requires 'first' and 'last' 
// properties whose values are strings
interface Person {
  first: string;
  last: string;
}

// This defines that the first functional argument 
// must be an Array of 'Person' objects, then destructs
// the first person's first and last name properties
const helloFirstPerson = ([{ first, last }]: Person[]) =>
  `Hello ${first} ${last}!`;

const people = [
  { first: 'John', last: 'Doe' },
  { first: 'Jane', last: 'Smith' }
];

// outputs "Hello John Doe!"
helloFirstPerson(people);

/* --------- Example of a Type Error ----------- */
// This creates an array argument that will be invalid for
// the helloFirstPerson() function, because there are no 'last'
// props on the 'people' objects
const badArgs = [{ first: 'John' }, { first: 'Jane' } ];

// Type Error! 
// Property 'last' is missing in type '{ first: string; }'
helloFirstPerson(badArgs);