unexpected typescript this is undefined type

Question

    /// <reference path="../typings/signalr/signalr.d.ts" />
/// <reference path="../typings/jquery/jquery.d.ts" />

interface IMyBlackjack {

}

module My {
    export class MyBlackjack implements IMyBlackjack {

        private hub: HubProxy;
        private cnn: HubConnection;

        constructor() {
            $("#formBlackJack").hide();

            this.cnn = $.hubConnection();
            this.hub = this.cnn.createHubProxy("blackjackHub");
            this.cnn.start(() => this.onConnStart);
        }

        private onConnStart(): void {
            $("#formBlackJack").show();
            this.hub.invoke('hello');
        }
    }
}

var myBlackjack: IMyBlackjack = new My.MyBlackjack();

there is a problem in the code:

this.hub.invoke('hello');

this.hub is surprisingly undefined.

And I hope it should be an object. Any thoughts about it ?

basarat · Accepted Answer · 2015-02-09 00:20:31Z

11

this is not pointing to the instance. Fix use a lambda:

    private onConnStart = () => {
        $("#formBlackJack").show();
        this.hub.invoke('hello');
    }

More: https://www.youtube.com/watch?v=tvocUcbCupA

also

this.cnn.start(() => this.onConnStart);

perhaps you meant to call i.e. () => this.onConnStart()

answered Feb 9, 2015 at 0:20

basarat

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2 Comments

alerya Over a year ago

Unfortunately, in your case onConnStart callback doesn't work. So there is a problem.

b26 Over a year ago

thanks for this. was scratching my head before. makes sense, but it also not consistent. cheers

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