node-get-random-values/polyfill.js

crypto.getRandomValues polyfill for node

import { randomBytes } from 'crypto';

/**
 * @param {TypedArray} ta 
 * @returns {(df: DataView, i: number) => number}
 */
const getMethod = (ta) => {
  if (ta instanceof Int8Array) return (df, i) => df.getInt8(i)
  if (ta instanceof Uint8Array) return (df, i) => df.getUint8(i)
  if (ta instanceof Uint8ClampedArray) return (df, i) => df.getUint8(i)
  if (ta instanceof Int16Array) return (df, i) => df.getInt16(i)
  if (ta instanceof Uint16Array) return (df, i) => df.getUint16(i)
  if (ta instanceof Int32Array) return (df, i) => df.getInt32(i)
  if (ta instanceof Uint32Array) return (df, i) => df.getUint32(i)
  if (ta instanceof Float32Array) return (df, i) => df.getFloat32(i)
  if (ta instanceof Float64Array) return (df, i) => df.getFloat64(i)
  if (ta instanceof BigInt64Array) return (df, i) => df.getBigInt64(i)
  if (ta instanceof BigUint64Array) return (df, i) => df.getBigUint64(i)
  throw Error('Unknown typed array')
}

/** 
 * @typedef {Int8Array|Uint8Array|Uint8ClampedArray|Int16Array|Uint16Array|Int32Array|Uint32Array|Float32Array|Float64Array} TypedArray
 */

global.crypto = { 
  /** 
   * Polyfill for `crypto.getRandomValues` for node, using node's `crypto` module.
   * @param {TypedArray} typedArray A typed array to be filled with random data.
   * @returns {TypedArray} The same typed array filled with random data.
   */
  getRandomValues(typedArray) {
    const { BYTES_PER_ELEMENT, length } = typedArray;
    const totalBytes = BYTES_PER_ELEMENT * length;
    const { buffer } = randomBytes(totalBytes);
    const dataView = new DataView(buffer);
    const method = getMethod(typedArray);
    for (let byteIndex = 0; byteIndex < totalBytes; byteIndex += BYTES_PER_ELEMENT) {
      const integer = method(dataView, byteIndex);
      const arrayIndex = byteIndex / BYTES_PER_ELEMENT;
      typedArray[arrayIndex] = integer;
    }
    return typedArray;
  }
};