functional programming - Why no Array.prototype.flatMap in javascript?

Question

flatMap is incredibly useful on collections, but javascript does not provide one while having Array.prototype.map. Why?

Is there any way to emulate flatMap in javascript in both easy and efficient way w/o defining flatMap manually?

Answer 1

Update: Array.prototype.flatMap made it into ES2019

It is widely supported in many environments. See if it works in your browser using this snippet below -

const data =
  [ 1, 2, 3, 4 ]
  
console.log(data.flatMap(x => Array(x).fill(x)))
// [ 1, 2, 2, 3, 3, 3, 4, 4, 4, 4 ]