爲什麼myVar未定義？

Question

當我得到我的插座事件drawMouse & my draw()功能被稱爲myVar是未定義的。 爲什麼我無法從socket.on回調中訪問this.myVar？

import { Component, OnInit } from '@angular/core'; 

import * as io from 'socket.io-client'; 


@Component({ 
    selector: 'app-test', 
    templateUrl: './test.component.html', 
    styleUrls: ['./test.component.css'] 
}) 
export class TestComponent implements OnInit { 
    myVar:string; 

    constructor(){ 
    this.socket = io("http://localhost:4300"); 
    this.myVar = "hello" 

    } 

    ngOnInit() { 
     this.socket.on('drawMouse', function(data){ 
      this.draw(data) 
     }) 
    } 

    draw(){ 
    //this variable is undefined 
    console.log(this.myVar); 
    } 
} 

Answer 1

因爲this插座回調裏面是不是指的組件。

嘗試：

this.socket.on('drawMouse', (data)=>{ 
      this.draw(data) 
     })