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📜  HTML5-CORS

📅  最后修改于: 2020-10-23 06:21:56             🧑  作者: Mango

跨域资源共享（CORS）是一种允许来自Web浏览器中另一个域的受限资源的机制。

假设，如果您在html5演示部分中单击HTML5-视频播放器。它将询问相机许可。如果用户允许该权限，则只有它会打开相机，否则不会为Web应用程序打开相机。

提出CORS要求

在这里，Chrome，Firefox，Opera和Safari都使用XMLHttprequest2对象，而Internet Explorer使用类似的XDomainRequest对象。

function createCORSRequest(method, url) {
   var xhr = new XMLHttpRequest();
   
   if ("withCredentials" in xhr) {
      
      // Check if the XMLHttpRequest object has a "withCredentials" property.
      // "withCredentials" only exists on XMLHTTPRequest2 objects.
      xhr.open(method, url, true);
   } else if (typeof XDomainRequest != "undefined") {
      
      // Otherwise, check if XDomainRequest.
      // XDomainRequest only exists in IE, and is IE's way of making CORS requests.
      xhr = new XDomainRequest();
      xhr.open(method, url);
   } else {
      
      // Otherwise, CORS is not supported by the browser.
      xhr = null;
   }
   return xhr;
}

var xhr = createCORSRequest('GET', url);

if (!xhr) {
   throw new Error('CORS not supported');
}

CORS中的事件句柄

Sr.No. Event Handler & Description
1

onloadstart

Starts the request
2

onprogress

Loads the data and send the data
3

onabort

Abort the request
4

onerror

request has failed
5

onload

request load successfully
6

ontimeout

time out has happened before request could complete
7

onloadend

When the request is complete either successful or failure

onload或onerror事件的示例

xhr.onload = function() {
   var responseText = xhr.responseText;
   
   // process the response.
   console.log(responseText);
};

xhr.onerror = function() {
   console.log('There was an error!');
};

带处理程序的CORS示例

下面的示例将显示makeCorsRequest（）和onload处理程序的示例

// Create the XHR object.
function createCORSRequest(method, url) {
   var xhr = new XMLHttpRequest();
   
   if ("withCredentials" in xhr) {
      
      // XHR for Chrome/Firefox/Opera/Safari.
      xhr.open(method, url, true);
   } else if (typeof XDomainRequest != "undefined") {
      
      // XDomainRequest for IE.
      xhr = new XDomainRequest();
      xhr.open(method, url);
   } else {
      
      // CORS not supported.
      xhr = null;
   }
   return xhr;
}

// Helper method to parse the title tag from the response.
function getTitle(text) {
   return text.match('(.*)?')[1];
}

// Make the actual CORS request.
function makeCorsRequest() {
   
   // All HTML5 Rocks properties support CORS.
   var url = 'http://www.tutorialspoint.com';
   
   var xhr = createCORSRequest('GET', url);
   
   if (!xhr) {
      alert('CORS not supported');
      return;
   }
   
   // Response handlers.
   xhr.onload = function() {
      var text = xhr.responseText;
      var title = getTitle(text);
      alert('Response from CORS request to ' + url + ': ' + title);
   };
   
   xhr.onerror = function() {
      alert('Woops, there was an error making the request.');
   };
   xhr.send();
}