canvas 图片显示问题

Question

    <canvas id="canvas" width="1000" height="500" style="background:#333"></canvas>

    //html代码

     var canvas = document.getElementById('canvas'),

        cvs = canvas.getContext('2d');

    (function motion(){

        cvs.clearRect(0,0,canvas.width,canvas.height);//为什么加上这条就无法显示图片了？

        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();