uniapp中如何使用laravel-echo,连接websocket服务

我后端用的php框架是laravel,引入下面代码：

import Echo from 'laravel-echo';  

window.Pusher = require('pusher-js');  

let laravelEcho = new Echo({  
    broadcaster: 'pusher',  
    key: process.env.MIX_PUSHER_APP_KEY,  
    wsHost: process.env.MIX_PUSHER_HOST,  
    wsPort: process.env.MIX_PUSHER_PORT,  
    wssPort: process.env.MIX_PUSHER_PORT,  
    forceTLS: false,  
    encrypted: true,  
    disableStats: true,  
    enabledTransports: ['ws', 'wss'],  
});  

laravelEcho.private(`orders.${orderId}`)  
    .listen('OrderShipmentStatusUpdated', (e) => {  
        console.log(e.order);  
    });

报错信息：

reportJSException >>>> exception function:createInstanceContext, exception:white screen cause create instanceContext failed,check js stack ->Uncaught TypeError: Cannot read property 'btoa' of undefined
at (app-service.js:138733:32)
at webpack_require (app-service.js:138068:31)
at (app-service.js:138455:31)
at webpack_require (app-service.js:138068:31)
at (app-service.js:138121:18)
at (app-service.js:138122:10)
at webpackUniversalModuleDefinition (app-service.js:138049:25)
at (app-service.js:138050:7)
at (app-service.js:142049:5)
at (app-service.js:194330:3)
网页端可以正常连接，在uni-app中就不行了，求大佬指点！！！