ios上的safari如何調用攝像頭調用攝像頭來獲取視頻流呢？

var domElement = document.createElement(video);
domElement.setAttribute(autoplay, );
domElement.setAttribute(muted, );
domElement.setAttribute(playsinline, );
domElement.style.width = document.documentElement.clientWidth + px;
domElement.style.height = document.documentElement.clientHeight + px;

// check API is available
if(navigator.mediaDevices === undefined || navigator.mediaDevices.enumerateDevices === undefined || navigator.mediaDevices.getUserMedia === undefined){
if(navigator.mediaDevices === undefined){
var fctName = navigator.mediaDevices;
}
else if(navigator.mediaDevices.enumerateDevices === undefined){
var fctName = navigator.mediaDevices.enumerateDevices;
}
else if(navigator.mediaDevices.getUserMedia === undefined){
var fctName = navigator.mediaDevices.getUserMedia;
}
else{
console.assert(false);
}
onError({
name: ,
message: WebRTC issue-! +fctName+ not present in your browser
});
return null;
}

// get available devices
navigator.mediaDevices.enumerateDevices().then(function(devices){

var userMediaConstraints = {
audio: false,
video: {
facingMode: environment,
}
}

// get a device which satisfy the constraints
navigator.mediaDevices.getUserMedia(userMediaConstraints).then(function success(stream){
domElement.srcObject = stream;
document.body.addEventListener(click, function(){
domElement.play();
});
// wait until the video stream is ready
var interval = setInterval(function(){
if(!domElement.videoWidth){
return;
}
stage.appendChild(domElement);
clearInterval(interval);
}, 1000/50);
}).catch(function(error){
onError({
name: error.name,
message: error.message
});
});
}).catch(function(error){
onError({
message: error.message
});
});