Javascript 数组和对象/类

Question

我试图在屏幕上显示三张扑克牌，由于某种原因，每次运行代码时都会出现类型错误，我已尝试了一切方法来尝试修复它，但没有任何效果。我认为问题出在数组/对象构造函数中，但我认为一切都在其中。

"use strict";

function main(){
var cvs = document.getElementById("foo");
var ctx = foo.getContext("2d");
function Card(posX, posY, imgX, imgY){
    this.posX = posX;
    this.posY = posY;
    this.imgX = imgX;
    this.imgY = imgY;
    this.width = 97;
    this.height = 129;
}
Card.img = new Image();
Card.img.src = "allcards.png";
var cards = [new Card(0,0,0,0), new Card(400,400,194,258), new Card(200,200,291,387)];
var greaterX = false;
var lessX = false;
var greaterY = false;
var lessY = false;
var offsetX;
var offsetY;
setInterval(draw, 10);

function draw(){
    ctx.fillStyle="rgb(0,255,255)";
    ctx.clearRect(0,0,600,600);
    ctx.drawImage(Card.img,cards[1].imgX,cards[1].imgY,Card.width,Card.height,cards[1].posX, cards[1].posY);
    ctx.drawImage(Card.img,cards[2].imgX,cards[2].imgY,Card.width,Card.height,cards[2].posX, cards[2].posY);
}

}

Answer 1

var ctx = foo.getContext("2d");

这不应该是

var ctx = cvs.getContext("2d");