javascript - 未捕获的类型错误 : Cannot read property 'getContext' of undefined

Question

运行脚本时出现此错误“未捕获类型错误:无法读取未定义的属性“getContext””。似乎变量“canvas”未定义，但我不明白为什么。

var world = {
    canvas: document.getElementById("myCanvas"),
    context: this.canvas.getContext("2d"),
    centerX: this.canvas.width / 2,
    centerY: this.canvas.height / 2,
    drawShape: function (shape) {
        if (typeof shape.draw() === "function")
            shape.draw();
    }
};

Answer 1

我在 world 文字之外声明了变量 canvas 并且它正在工作