cors

CORS is a node.js package for providing a connect/express middleware that can be used to enable CORS with various options.

• Installation
• Usage
  • Simple Usage
  • Configuring CORS
  • Configuring CORS Asynchronously
• Configuration Options
• License
• Author

Installation (via npm)

$ npm install cors

Usage

Simple Usage (Enable All CORS Requests)

var express = require('express')
  , cors = require('cors')
  , app = express();
 
app.get('/products/:id', cors(), function(req, res, next){
  res.json({msg: 'This is CORS-enabled for all origins!'});
});
 
app.listen(80, function(){
  console.log('CORS-enabled web server listening on port 80');
});

Configuring CORS

var express = require('express')
  , cors = require('cors')
  , app = express();
 
var corsOptions = {
  origin: 'http://example.com'
};
 
app.get('/products/:id', cors(corsOptions), function(req, res, next){
  res.json({msg: 'This is CORS-enabled for only example.com.'});
});
 
app.listen(80, function(){
  console.log('CORS-enabled web server listening on port 80');
});

Configuring CORS Asynchronously

var express = require('express')
  , cors = require('cors')
  , app = express();
 
var whitelist = ['http://example1.com', 'http://example2.com'];
var corsOptionsDelegate = function(req, callback){
  var corsOptions;
  if(whitelist.indexOf(req.header('Origin')) !== -1){
    corsOptions = { origin: true }; // reflect (enable) the requested origin in the CORS response
  }else{
    corsOptions = { origin: false }; // disable CORS for this request
  }
  callback(null, corsOptions); // callback expects two parameters: error and options
};
 
app.get('/products/:id', cors(corsOptionsDelegate), function(req, res, next){
  res.json({msg: 'This is CORS-enabled for a whitelisted domain.'});
});
 
app.listen(80, function(){
  console.log('CORS-enabled web server listening on port 80');
});

Enabling CORS Pre-Flight

Certain CORS requests are considered 'complex' and require an initial OPTIONS request (called the "pre-flight request"). An example of a 'complex' CORS request is one that uses an HTTP verb other than GET/HEAD/POST (such as DELETE) or that uses custom headers. To enable preflighting, you must add a new OPTIONS handler for the route you want to support:

var express = require('express')
  , cors = require('cors')
  , app = express();
 
app.options('/products/:id', cors()); // enable preflight request for DELETE request
app.del('/products/:id', cors(), function(req, res, next){
  res.json({msg: 'This is CORS-enabled for all origins!'});
});
 
app.listen(80, function(){
  console.log('CORS-enabled web server listening on port 80');
});

Configuration Options

• origin: Configures the Access-Control-Allow-Origin CORS header. Expects a string (ex: "http://example.com"). Set to true to reflect the request origin, as defined by req.header('Origin'). Set to false to disable CORS.
• methods: Configures the Access-Control-Allow-Methods CORS header. Expects a comma-delimited string (ex: 'GET,PUT,POST') or an array (ex: ['GET', 'PUT', 'POST']).
• headers: Configures the Access-Control-Allow-Headers CORS header. Expects a comma-delimited string (ex: 'Content-Type,Authorization') or an array (ex: ['Content-Type', 'Authorization]). If not specified, defaults to reflecting the headers specified in the request's Access-Control-Request-Headers header.
• credentials: Configures the Access-Control-Allow-Credentials CORS header. Set to true to pass the header, otherwise it is omitted.
• maxAge: Configures the Access-Control-Allow-Max-Age CORS header. Set to an integer to pass the header, otherwise it is omitted.

For details on the effect of each CORS header, read this article on HTML5 Rocks.

License

MIT License

Author

Troy Goode ([e-mail])