调用本地摄像头并通过canvas拍照

首先我们需要新建一个video标签，并且放到html里边

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

document.body.appendChild(video);

 利用navigator对象

 navigator.mediaDevices.getUserMedia({
　　audio:true,
　　video:true
})

 这样就调用了摄像头和录音器

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

 利用video的srcObject属性和promise的then方法，把开启摄像头后的返回值给video标签，就显示出来了

全部的实现代码如下：

var video = document.createElement("video");
video.autoplay="autoplay";
document.body.appendChild(video);
navigator.mediaDevices.getUserMedia({
    audio: false, video: true
}).then(function (result) {
    video.srcObject = result;
})

 现在我们继续写canvas拍照的步骤

<video id='myVideo' hidden></video>
<canvas id='snap' width='500' height='500' style="border:1px solid #ccc"></canvas>
<button id='control'>拍照</button>
<script>
var snap = document.getElementById('snap');
var context = snap.getContext('2d');
var videoSrc = null;
navigator.mediaDevices.getUserMedia({
    audio: false, video: true
}).then(function (result) {
    videoSrc = result;
    console.log(videoSrc)
    myVideo.srcObject = videoSrc;
})
control.addEventListener('click',function(){  
    context.drawImage(myVideo,0,0,500,500);
    console.log(navigator.mediaDevices)
})
</script>

新建canvas画布，获得context

隐藏video

canvas.drawImage方法的第一个参数放video即可调用canvas拍照