我看到這個(gè)問題以前被問過，但它并沒有解決我的問題！我是 JavaScript 新手，我?guī)缀趸艘惶鞎r(shí)間嘗試解決它，但仍然無法解決。我有一個(gè)這樣的類和函數(shù)：let playerTank = {width: 80, height: 80, speed: 2};class Tank {    constructor(canvas) {        this.canvas = canvas;        this.ctx = canvas.getContext("2d");    }    draw() {        this.ctx.drawImage(.....);        this.ctx.stroke();    }    update(e) {        if (e.keyCode == 37) {            this.ctx.clearRect(0, 0, this.canvas.width, this.canvas.height);            this.draw();            // do something ...        }    }}function main() {    let canvas = document.getElementByID("my-canvas");        let tank = new Tank(canvas);    tank.draw();    window.addEventListener("keydown", tank.update, true);    window.addEventListener("keyup", tank.update, false);}main();這是我的問題！當(dāng)我單擊該鍵時(shí)，我會(huì)收到以下錯(cuò)誤：can't read property 'clearRect' of undefinedcan't read property 'draw' of undefined我實(shí)在不明白為什么不能訪問同一個(gè)類中的屬性和函數(shù)？