Array.prototype.reduce() - JavaScript
let myarray = ['a', 'b', 'a', 'b', 'c', 'e', 'e', 'c', 'd', 'd', 'd', 'd'] let myorderedarray = myarray.reduce(function (accumulator, currentvalue) { if (accumulator.indexof(currentvalue) === -1) { accumulator.push(currentvalue) } return accumulator }, []) console.log(myorderedarray) replace .filter().map() with .reduce() using array.filter() then array.map() traverses the array twice, but you can achieve the same effect while traversing only once with array.reduce(), thereby being more efficient.