HTML5 - CORS

Cross-origin resource sharing (CORS) is a mechanism to allows the restricted resources from another domain in web browser.

For suppose, if you cpck on HTML5- video player in html5 demo sections. it will ask camera permission. if user allow the permission then only it will open the camera or else it doesn t open the camera for web apppcations.

Making a CORS request

Here Chrome, Firefox, Opera and Safari all use the XMLHttprequest2 object and Internet Explorer uses the similar XDomainRequest object, object.

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 );
}

Event handles in CORS

Example of onload or onerror event

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

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

Example of CORS with handler

Below example will show the example of makeCorsRequest() and onload handler

// 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( <title>(.*)?</title> )[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();
}