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body {
  padding: 20px;
}
console.clear();

let items = ['a', 1, 'a', 'beachfront', 'avenue'];

let unique = items.reduce(function(a,b) {
  if (a.indexOf(b) < 0 ) {
    a.push(b);
  }
  return a;
},[]);

console.log(items); // original array
console.log(unique); // duplicates removed

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