javascript实现拍照功能详细示例代码

 <video id="video" autoplay></video>

const videoConstraints = { width: 1366, height: 768 };
const videoNode = document.querySelector('#video');
let stream = await navigator.mediaDevices.getUserMedia({ audio: true, video: videoConstraints });
videoNode.srcObject = stream;
videoNode.play();

// enumerateDevices获取所有媒体设备
const mediaDevices = await navigator.mediaDevices.enumerateDevices();

// 通过设备实例king属性videoinput，过滤获取摄像头设备
const videoDevices = mediaDevices.filter(item => item.kind === 'videoinput') || [];

// 获取前置摄像头
const videoDeviceId = videoDevices[0].deviceId;
const videoConstraints = { deviceId: { exact: videoDeviceId }, width: 1366, height: 768 };
let stream = await navigator.mediaDevices.getUserMedia({ audio: true, video: videoConstraints });

// 获取后置摄像头
const videoDeviceId = videoDevices[1].deviceId;
const videoConstraints = { deviceId: { exact: videoDeviceId }, width: 1366, height: 768 };
let stream = await navigator.mediaDevices.getUserMedia({ audio: true, video: videoConstraints });

// 依次类推...

// 通过canvas捕捉video流，生成base64格式图片
const canvas = document.createElement('canvas');
const context = canvas.getContext('2d');
canvas.width = 1366;
canvas.height = 768;
context.drawImage(videoNode, 0, 0, canvas.width, canvas.height);
download(canvas.toDataURL('image/jpeg'));

// 下载图片
function download (src) {
   if (!src) return;
   const a = document.createElement('a');
   a.setAttribute('download', new Date());
   a.href = src;
   a.click();
}

let stream = await navigator.mediaDevices.getUserMedia({ audio: true, video: videoConstraints });
// 3s后关闭摄像头
setTimeout(function () {
    stream.getTracks().forEach(track => track.stop());
    stream = null;
}, 3000);