prototype.js

Array.prototype.uniq = function(key) {
  return key
    ? this.map(e => e[key])
        .map((e, i, final) => final.indexOf(e) === i && i)
        .filter(e => this[e])
        .map(e => this[e])
    : [...new Set(this)];
}

Array.prototype.asyncMap = async function(func) {
  const data = []

  for (let item of this) {
    data.push(await func(item))
  }

  return data
}

Array.prototype._concat = function() {
  return this.reduce((prev, next) => prev.concat(next), [])
}