Weighted random value in ES6

random-weighted-es6.js

// Defined first due to TDZ

let weighted = (...weightMap) => weightMap
  .map(({0: value, 1: weight}) => new Array(weight).fill(value))
  .reduce((acc, current) => [...acc, ...current]);

let random = (array) => array[Math.floor(Math.random() * array.length)];


// You can generate a weighted array

weighted([true, 1], [false, 2]); // [true, false, false]

weighted([true, 1], [false, 3]); // [true, false, false, false]

// Then random picks one randomly
// The following will return true or false with a 1:3 ratio

random(weighted([true, 1], [false, 3]));