JQuery-alike JSON client API. Includes promises and cross-browser compatibility.

gistfile1.js

define('json-client', function() {

  var JSON_KEY;

  var API_BASE = '';

  var validResponses = {
    200: true,
    201: true,
    204: true
  };

  var invalidResponses = {
    400: true,
    401: true,
    404: true,
    500: true
  };

  var XMLHttpFactories = [
    function() {
      return new XMLHttpRequest();
    },
    function() {
      return new ActiveXObject('Msxml2.XMLHTTP');
    },
    function() {
      return new ActiveXObject('Msxml3.XMLHTTP');
    },
    function() {
      return new ActiveXObject('Microsoft.XMLHTTP');
    }
  ];

  function createXMLHTTPObject() {
    var xmlhttp = false;
    for (var i = 0; i < XMLHttpFactories.length; i++) {
      try {
        xmlhttp = XMLHttpFactories[i]();
      } catch (e) {
        continue;
      }
      break;
    }
    return xmlhttp;
  }

  function xhr(options) {

    var success = options.success || function() {};
    var error = options.error || function() {};
    var req = createXMLHTTPObject();

  	var promise = {
			promises: {success:[],failure:[]},
			then: function (success, failure) {
				if (success)  this.promises.success.push(success);
				if (failure)  this.promises.failure.push(failure);
				return this;
			},
			fail: function (response) {
				for (var i = 0; i < this.promises.failure.length; i++) {
					this.promises.failure[i](response);
				}
			},
			succeed: function (response) {
				for (var i = 0; i < this.promises.success.length; i++) {
					this.promises.success[i](response);
				}
			}
		}
		promise.then(success, error);

    req.open(options.method, API_BASE + options.url, true);

    options.headers = options.headers || {};
    options.headers['Content-Type'] = 'application/json';
    options.headers['Accept'] = 'application/json';

    if (JSON_KEY) {
      options.headers['X-JSON-Key'] = JSON_KEY;
    }

    for (var k in options.headers) {
      req.setRequestHeader(k, options.headers[k]);
    }

    req.onreadystatechange = function() {
      if (req.readyState !== 4) {
        return;
      }

      if (req.status == 0) {
				promise.fail('Server failed to respond.');
				return;
			}
      if ((req.status in invalidResponses) && !(req.status in validResponses)) {
				var response = req.responseText;
				try {
					response = JSON.parse(response);
					promise.fail(response);
				} catch(e) {
					promise.fail('Internal failure: expected JSON.');
				}
				return;
      }

      if (req.getResponseHeader('X-New-JSON-Key')) {
        JSON_KEY = req.getResponseHeader('X-New-JSON-Key');
      }

      var response = req.responseText;
      response = JSON.parse(response);
      promise.succeed(response);
    };

    if (req.readyState === 4) {
      return;
    }

    req.send(options.data || null);
		return promise;
  }

  function get(options) {
    options.method = 'GET';
    return xhr(options);
  }

  function post(options) {
    options.method = 'POST';
    options.data = JSON.stringify(options.data || {});
    return xhr(options);
  }

  function put(options) {
    options.method = 'PUT';
    options.data = JSON.stringify(options.data || {});
    return xhr(options);
  }

  return {
    get: get,
    post: post,
    put: put
  };

});