js 使用摄像头进行拍照上传功能

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>js开启摄像头拍照并上传图片</title>
</head>
<body>

<video id="video" width="640" height="480" autoplay="autoplay"></video>
<canvas id="canvas" style="display: none;" width="640" height="480"></canvas>
<button onclick="openMedia()">开启摄像头</button>
<button id="capture" onclick="takePhoto()">拍照</button>
<button onclick="closeMedia()">关闭摄像头</button>
<div><img id="imgTag" src="" alt="imgTag"></div>
<script>
  let video = document.getElementById("video");
  let canvas = document.getElementById("canvas");
  let context = canvas.getContext("2d");
  // 开启摄像头
  function openMedia() {
     // 老的浏览器可能根本没有实现 mediaDevices，所以我们可以先设置一个空的对象
     if (navigator.mediaDevices === undefined) {
        navigator.mediaDevices = {};
    }
    // 一些浏览器部分支持 mediaDevices。我们不能直接给对象设置 getUserMedia
    // 因为这样可能会覆盖已有的属性。这里我们只会在没有getUserMedia属性的时候添加它。
    if (navigator.mediaDevices.getUserMedia === undefined) {
        navigator.mediaDevices.getUserMedia = function (constraints) {

            // 首先，如果有getUserMedia的话，就获得它
            var getUserMedia = navigator.webkitGetUserMedia || navigator.mozGetUserMedia;

            // 一些浏览器根本没实现它 - 那么就返回一个error到promise的reject来保持一个统一的接口
            if (!getUserMedia) {
                return Promise.reject(new Error('getUserMedia is not implemented in this browser'));
            }

            // 否则，为老的navigator.getUserMedia方法包裹一个Promise
            return new Promise(function (resolve, reject) {
                getUserMedia.call(navigator, constraints, resolve, reject);
            });
        }
    }
    //默认使用前摄像头，强制使用后置摄像头如下设置
    // let constraints = {video: { facingMode: { exact: "environment" } }};
    let constraints = {video: true};
    navigator.mediaDevices.getUserMedia(constraints)
        .then(function (stream) {
            // 旧的浏览器可能没有srcObject
            if ("srcObject" in video) {
                video.srcObject = stream;
            } else {
                // 防止在新的浏览器里使用它，应为它已经不再支持了
                video.src = window.URL.createObjectURL(stream);
            }
            video.onloadedmetadata = function (e) {
                video.play();
            };
        })
        .catch(function (err) {
            console.log(err.name + ": " + err.message);
        });
  }
  // 拍照
  function takePhoto() {
    //绘制画面
    context.drawImage(video, 0, 0, 640, 480);
    // toDataURL  ---  可传入'image/png'---默认, 'image/jpeg'
    let img = document.getElementById('canvas').toDataURL();
        // 这里的img就是得到的图片
    console.log('img-----', img);
    document.getElementById('imgTag').src=img;
  }
  // 关闭摄像头
  function closeMedia() {
    if("srcObject" in video) {
      let stream = video.srcObject;
      let tracks = stream.getTracks();
      tracks.forEach(function(track) {
            track.stop();
          });
      video.srcObject = null;
    }
  }
</script>
</body>
</html>
参考：
https://www.cnblogs.com/cangqinglang/p/10210826.html