canvas打开本机摄像头

 (function () {

     var video = document.createElement("video");
     video.autoplay="autoplay";
     document.body.appendChild(video);

     function init() {
         navigator.mediaDevices.getUserMedia({
             audio: false, video: true
         }).then(function (result) {
             video.srcObject = result;
         }).catch(function (error) {
             console.log(error);
         })
     }

     init();
 })();