Lightweight module to pick a random element from a weighted array

random-weighted-picker.js

class Picker {
  /**
  * @param {Function} [randomFn] Random number generator
  */
  constructor(randomFn = Math.random) {
    this.random = randomFn;
  }

  /**
  * Pick a random value based on its weight.
  * @param {Array} data Array of values.
  * @return {Mixed}
  */
  pick(data) {
    if (!Array.isArray(data) || data.length === 0) {
      throw new TypeError('Expected a non-empty Array as the first argument');
    }

    const totalWeight = data.reduce((sum, item) => sum + item[1], 0);
    const rand = this.random() * totalWeight;

    let weightSum = 0;
    for (const [value, weight] of data) {
      weightSum += weight;
      if (rand <= weightSum) {
        return value;
      }
    }

    // Fallback in case of unexpected error
    return data[data.length - 1][0];
  }
}

const pick = (data, randomFn) => {
  const picker = new Picker(randomFn);
  return picker.pick(data);
};

export default pick;
export { pick, Picker };