javascript - 为什么es6需要构造函数？

Question

为什么当我在测试id中写入'new ServerNotificationApi'时不会调用构造函数，对我来说new ServerNotificationApi.constructor()有效，但我无法理解为什么当我写入new ServerNotificationApi时 我在单元测试中遇到错误“TypeError: _serverNotifications.default is not a constructor”

类

class ServerNotificationApi {
        constructor() {
            SignalR.initConnection(url.serverNotificationHubName)
        }

        subscribe = callback => SignalR.subscribe(url.entityChanged, url.serverNotificationHubName, callback);

        unsubscribe = callback => SignalR.unsubscribe(url.entityChanged, url.serverNotificationHubName, callback);
    }

    export default new ServerNotificationApi()

测试

 it('constructor should call signalR method \'initConnection\'', () => {
        sinon.stub(SignalR, 'initConnection')

        new ServerNotificationApi.constructor()

    SignalR.initConnection.calledWith(url.serverNotificationHubName).should.be.true

        SignalR.initConnection.restore()
    })

Answer 1

export default new ServerNotificationApi()
               ↑↑↑

您正在导出类的实例，而不是类本身。你本质上是在做:

let foo = new ServerNotificationApi();
new foo();

是的，这不起作用。删除export中的new。