How to create a list of unique items in JavaScript?

Question

In my CouchDB reduce function I need to reduce a list of items to the unique ones.

Note: In that case it\'s ok to have a list, it will be a small number of items

Answer 1

I find the other answers to be rather complicated for no gain that I can see.

We can use the indexOf method of the Array to verify if an item exists in it before pushing:

const duplicated_values = ['one', 'one', 'one', 'one', 'two', 'three', 'three', 'four'];
const unique_list = [];

duplicated_values.forEach(value => {
  if (unique_list.indexOf(value) === -1) {
    unique_list.push(value);
  }
});

console.log(unique_list);

That will work with any type of variable as well, even objects (given the identifier actually reference the same entity, merely equivalent objects are not seen as the same).