ethers.js/utils/browser-random-bytes.js

'use strict';

var defineProperty = require('./properties.js').defineProperty;

var crypto = global.crypto || global.msCrypto;
if (!crypto || !crypto.getRandomValues) {
    console.log('WARNING: Missing strong random number source; using weak randomBytes');
    crypto = {
        getRandomValues: function(buffer) {
            for (var round = 0; round < 20; round++) {
                for (var i = 0; i < buffer.length; i++) {
                    if (round) {
                        buffer[i] ^= parseInt(256 * Math.random());
                    } else {
                        buffer[i] = parseInt(256 * Math.random());
                    }
                }
            }

            return buffer;
        },
        _weakCrypto: true
    };
} else {
    console.log('Found strong random number source');
}

function randomBytes(length) {
    if (length <= 0 || length > 1024 || parseInt(length) != length) {
        throw new Error('invalid length');
    }

    var result = new Uint8Array(length);
    crypto.getRandomValues(result);
    return result;
};

if (crypto._weakCrypto === true) {
    defineProperty(randomBytes, '_weakCrypto', true);
}

module.exports = randomBytes;