example.js

const sample = require("lodash/sample");
const flatMapDeep = require("lodash/flatMapDeep");

const lineCollection = [
  { symbol: "■", rarity: 25 },
  { symbol: "─", rarity: 25 },
  { symbol: "=", rarity: 20 },
  { symbol: "-=", rarity: 20 },
  { symbol: "✦", rarity: 20 },
  { symbol: "<>", rarity: 20 },
  { symbol: "░", rarity: 15 },
  { symbol: " ", rarity: 10 },
  { symbol: "/\\", rarity: 10 },
  { symbol: "↯ ", rarity: 10 },
  { symbol: "★ ", rarity: 10 },
  { symbol: "■ ", rarity: 5 },
  { symbol: "∆ ", rarity: 5 },
  { symbol: "😊  ", rarity: 3 },
  { symbol: "♥ ", rarity: 1 }
];

const line = sample(
  flatMapDeep(lineCollection, line => Array(line.rarity).fill(line.symbol))
);