var params = {
    type: 'wechat',
    partnerid: '10000100', // merchant id
    prepayid: 'wx201411101639507cbf6ffd8b0779950874', // prepay id
    noncestr: '1add1a30ac87aa2db72f57a2375d8fec', // nonce
    timestamp: '1439531364', // timestamp
    sign: '0CB01533B8C1EF103065174F50BCA001', // signed string
};

xpay(params, function() {
    console.log('success');
}, function (error) {
    console.log(error);
});

var params = {
    type: 'alipay',
    order: 'alipay_sdk=alipay-sdk-java-dynamicVersionNo&app_id=2017062907602740&...', // this string return by back-end
}

xpay(params, function() {
    console.log('success');
}, function (error) {
    console.log(error);
});