simple-chart.js

const generateGraph = (data, {
  includeZero = true,
  useMin = true,
  length = 10,
} = {}) => {
  const chars = (includeZero ? ' ' : '') + '▁▂▃▄▅▆▇█';
  const aggregated = length ? data.reduce((out, point, i) => {
    const ri = Math.floor(i / (data.length / length));
    out[ri] = out[ri] || [];
    out[ri].push(point);
    return out;
  }, []).map(a => {
    return a.reduce((out, p) => out + p, 0) / a.length;
  }) : data;
  const max = aggregated.reduce((max, c) => Math.max(max, c), 0);
  const min = useMin ? aggregated.reduce((min, c) => Math.min(min, c), 99999999) : 0;
  const normalized = aggregated.map(p => Math.round(((p / max) - min) * (chars.length - 1)));
  return normalized.map(i => chars[i]).join('');
};

const data = new Array(30).fill(undefined).map(() => Math.random());
console.log(generateGraph(data));