Qwest is a simple ajax library based on promises and that supports XmlHttpRequest2 special data like ArrayBuffer, Blob and FormData.

You can pick the minified library or install it with :

npm install qwest
bower install qwest
jam install qwest

The qwest.min.js file has been bundled to work in any environment. But if you don't want to load qwest and its dependencies, you can use src/qwest.js as a CommonJS module.

It should work in web workers too, but please not XML response data can't be handled since DOMParser is not available on the worker.

A good effort has been made to make qwest usable in any environment, including : the browser, require.js, browserify and web workers. It should work in any other CommonJS loader.

qwest.get('example.com')
	 .then(function(xhr, response) {
		alert(response);
	 });

qwest.post('example.com', {
		firstname: 'Pedro',
		lastname: 'Sanchez',
		age: 30
	 })
	 .then(function(xhr, response) {
		// Make some useful actions
	 })
	 .catch(function(xhr, response, e) {
		// Process the error
	 });

qwest.`method`(`url`, `data`, `options`, `before`)
	 .then(function(xhr, response) {
		// Run when the request is successful
	 })
	 .catch(function(xhr, response, e) {
		// Process the error
	 })
	 .complete(function(xhr, response) {
		// Always run
	 });

The method is either get, post, put or delete. The data parameter can be a multi-dimensional array or object, a string, an ArrayBuffer, a Blob, etc... If you don't want to pass any data but specify some options, set data to null.

The available options are :

• dataType : post (by default), json, text, arraybuffer, blob, document or formdata (you don't need to specify XHR2 types since they're automatically detected)
• responseType : the response type; either auto (default), json, xml, text, arraybuffer, blob or document
• cache : browser caching; default is false
• async : true (default) or false; used to make asynchronous or synchronous requests
• user : the user to access to the URL, if needed
• password : the password to access to the URL, if needed
• headers : javascript object containing headers to be sent
• withCredentials : false by default; sends credentials with your XHR2 request (more info in that post)
• timeout : the timeout for the request in ms; 30000 by default
• attempts : the total number of times to attempt the request through timeouts; 1 by default; if you want to remove the limit set it to null
• pinkyswear : override promise methods (experimental)

You can change the default data type with :

qwest.setDefaultDataType('json');

If you want to make a call with another HTTP method, you can use the map() function :

qwest.map('PATCH', 'example.com')
	 .then(function() {
	 	// Blah blah
	 });

If you need to do a sync request, you must call send() at the end of your promise :

qwest.get('example.com', {async: false})
	 .then(function() {
	 	// Blah blah
	 })
	 .send();

You can define a base URI for your requests. The string will be prepended to the other request URIs.

qwest.base = 'http://example.com';

// Will make a request to 'http://example.com/somepage'
qwest.get('/somepage')
	 .then(function() {
	 	// Blah blah
	 });

One of the greatest qwest functionnalities is the request limit. It avoids browser freezes and server overloads by freeing bandwidth and memory resources when you have a whole bunch of requests to do at the same time. Set the request limit and when the count is reached qwest will stock all further requests and start them when a slot is free.

Let's say we have a gallery with a lot of images to load. We don't want the browser to download all images at the same time to have a faster loading. Let's see how we can do that.

<div class="gallery">
	<img data-src="images/image1.jpg" alt="">
	<img data-src="images/image2.jpg" alt="">
	<img data-src="images/image3.jpg" alt="">
	<img data-src="images/image4.jpg" alt="">
	<img data-src="images/image5.jpg" alt="">
	...
</div>

// Browsers are limited in number of parallel downloads, setting it to 4 seems fair
qwest.limit(4);

$('.gallery').children().forEach(function() {
	var $this = $(this);
	qwest.get($this.data('src'), {responseType: 'blob'})
		 .then(function(xhr, response) {
			$this.attr('src', window.URL.createObjectURL(response));
			$this.fadeIn();
		 });
});

If you want to remove the limit, set it to null.

If you want to apply some manual options to the XHR object, you can use the before option

qwest.get('example.com', null, null, function(xhr) {
		xhr.uploadonprogress = function(e) {
			// Upload in progress
		};
	 })
	 .then(function(xhr, response) {
		// Blah blah blah
	 });

XHR2 is not available on every browser, so, if needed, you can simply verify the XHR version with :

if(qwest.xhr2) {
	// Actions for XHR2
}
else {
	// Actions for XHR1
}

Getting binary data in legacy browsers needs a trick, as we can read it on MDN. In qwest, that's how we could handle it :

qwest.get('example.com/file', null, null, function(xhr) {
		xhr.overrideMimeType('text\/plain; charset=x-user-defined');
	 })
	 .then(function(response) {
	 	// response is now a binary string
	 });

According to this compatibility table, IE7/8 do not support using catch and delete as method name because these are reserved words. If you want to support those browsers you should write :

qwest.delete('example.com')
	 .then(function(){})
	 .catch(function(){});

Like this :

qwest['delete']('example.com')
	 .then(function(){})
	 ['catch'](function(){});

XHR2 does not support arraybuffer, blob and document response types in synchroneous mode.

The CORS object shipped with IE8 and 9 is XDomainRequest. This object does not support PUT and DELETE requests and XHR2 types. Moreover, the getResponseHeader() method is not supported too which is used in the auto mode for detecting the reponse type. Then, the response type automatically fallbacks to json when in auto mode. If you expect another response type, please specify it explicitly. If you want to specify another default response type to fallback in auto mode, you can do it like this :

qwest.setDefaultXdrResponseType('text');

• the catch handler will be executed for status codes different from 2xx; if no data has been received when catch is called, response will be null
• auto mode is only supported for xml, json and text response types; for arraybuffer, blob and document you'll need to define explicitly the responseType option
• if the response of your request doesn't return a valid (and recognized) Content-Type header, then you must explicitly set the responseType option
• if an error occurs in a then() callback, it will be caught by the catch() promise
• the default Content-Type header is application/x-www-form-urlencoded for post and xhr2 data types, with a POST request
• if you want to set or get raw data, set dataType option to text
• as stated on StackOverflow, XDomainRequest forbid HTTPS requests from HTTP scheme and vice versa
• promises are asynchroneous, even with sync requests
• IE8 only support basic request's methods

MIT license everywhere!