<canvas id="canvas" width="1000" height="500" style="background:#333"></canvas>    //html代碼     var canvas = document.getElementById('canvas'),        cvs = canvas.getContext('2d');    (function motion(){        cvs.clearRect(0,0,canvas.width,canvas.height);//為什么加上這條就無法顯示圖片了？        img();        console.log(1)        requestAnimationFrame(motion);    })();    function img(){        var Img = new Image();        Img.src = 'https://www.baidu.com/img/bd_logo1.png';        Img.onload = function(){            cvs.drawImage(Img,100,100);        };    };    img();