randomhex/src/index.js

var randomHex = function(size, callback) {
    var crypto = require('./crypto.js');
    var isCallback = (typeof callback === 'function');

    
    if (size > 65536) {
        if(isCallback) {
            callback(new Error('Requested too many random bytes.'));
        } else {
            throw new Error('Requested too many random bytes.');
        }
    };


    // is node
    if (typeof crypto !== 'undefined' && crypto.randomBytes) {

        if(isCallback) {
            crypto.randomBytes(size, function(err, result){
                if(!err) {
                    callback(null, '0x'+ result.toString('hex'));
                } else {
                    callback(error);
                }
            })
        } else {
            return '0x'+ crypto.randomBytes(size).toString('hex');
        }

    // is browser
    } else {
        var cryptoLib;

        if (typeof crypto !== 'undefined') {
            cryptoLib = crypto;
        } else if(typeof msCrypto !== 'undefined') {
            cryptoLib = msCrypto;
        }

        if (cryptoLib && cryptoLib.getRandomValues) {
            var randomBytes = cryptoLib.getRandomValues(new Uint8Array(size));
            var returnValue = '0x'+ Array.from(randomBytes).map(function(arr){ return arr.toString(16); }).join('');

            if(isCallback) {
                callback(null, returnValue);
            } else {
                return returnValue;
            }

        // not crypto object
        } else {
            var error = new Error('No "crypto" object available. This Browser doesn\'t support generating secure random bytes.');

            if(isCallback) {
                callback(error);
            } else {
               throw error;
            }
        }
    }
};


module.exports = randomHex;