[ES6] Return distinct items in an iterable by using a specific key selector for equality checking. Only the first item of each key is returned.

distict-by.js

function* distinctBy(iterable, keySelector) {
  const keys = new Set();
  
  for (const item of iterable) {
    const key = keySelector(item);
    if (!keys.has(key)) { 
      keys.add(key); 
      
      yield item;
    }
  }
}

const items = [
  { id: 1, name: 'André' },
  { id: 2, name: 'Filipe' },
  { id: 2, name: 'Paulo' }  // will be ignored
];

console.log(Array.from(distinctBy(items, i => i.id)));