To check if an array item is set in JavaScript, we use the in operator.

For instance, we write

const assocPagine = {
  home: 0,
  about: 1,
  work: 2,
};

if ("work" in assocPagine) {
  // ...
}

to check if the work property is in the assocPagine object as a property in the object itself or as an inherited property.