Debugging Challenge #2

Previously on Dr. Lambda's blog:

I have deviced a series of debugging challenges, some are easy, some are really hard, all come from real live systems. Good luck!

The Challenge

• 1 point if you can spot where the error is.
• +1 point if you can explain why.
• +2 points if you can explain how to fix it.

export class ActivityService {
    activities : Activity[] = [];
    constructor(){
        this.activities = [
            {
                title: "Arrange meeting",
                type: "task"
            }
        ];
        setTimeout(function () {
            this.activities.push({ 
                title: "Meeting",
                type: "appointment"
            });
        }, 3000); 
    };
}