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dojo/request

authors:Bryan Forbes
since:V1.8

dojo/request is a package which provides asynchronous requests in a cross platform way. This is commonly referred to as AJAX.

Introduction

dojo/request is comprised of several modules that provide functionality around asynchronous requests. It leverages the dojo/promise API to manage the asynchronous communication. The concept is that a request has a provider. The providers behave in similar way and have the same core API, but may add additional interfaces as needed to fully support the functionality of the particular type of provider. The following providers are available in dojo/request:

  • dojo/request/xhr - Provides a cross browser compatible XmlHttpRequest. It is the default provider for browser platforms.
  • dojo/request/node - Provides an asynchronous request for node.js. It is the default provider for node.js.
  • dojo/request/iframe - Provides an IFrame transport for the asynchronous request. This is useful in situations where files need to be submitted or certain cross domain situations.
  • dojo/request/script - Provides a transport where the return payload is expected to be embedded in a <script> tag.

By requiring the dojo/request module, it will return the default provider for the current platform.

Once the request is fulfilled, the response can be handled by a handler. dojo/request provides the following handlers as a default:

  • json - The response is expected to be JSON and is converted to an object.
  • xml - The response is expected to be XML and is converted to an object.
  • javascript - The response is expected to be JavaScript and eval() is used against the response.

In addition, dojo/request/handlers provides a mechanism to register additional handlers that then can be used to deal with different types of responses.

There are a few modules as part of the package which assist in managing requests:

  • dojo/request/notify - Provides an dojo/Evented interface for global request event notification.
  • dojo/request/registry - Allows registering different providers by a URI pattern, so that different providers can be used based on the target URI without the user having to code separate code paths.

Usage

Requiring the dojo/request module returns the default provider, so in most cases, all you need to do is simply require that module and specify the resource you need. The most basic usage would look like this:

require(["dojo/request"], function(request){
  request("request.html").then(function(data){
    // do something with handled data
  }, function(err){
    // handle an error condition
  }, function(evt){
    // handle a progress event
  });
});

If the above was on a browser, dojo/request/xhr would have been used and if it was on node.js, dojo/request/node would have been used.

Providers take two arguments:

Argument Type Description
url String The URL the request should be made to
options Object? Optional A hash of any options for the provider.

The options argument is dependent upon the provider, but some common options are:

Property Type Default Description
data String|Object null Data, if any, that should be sent with the request.
query String|Object null The query string, if any, that should be sent with the request.
preventCache Boolean false If true will send an extra query parameter to ensure the the server won’t supply cached values.
method String GET The HTTP method that should be used to send the request.
timeout Integer null The number of milliseconds to wait for the response. If this time passes the request is canceled and the promise rejected.
handleAs String text The content handler to process the response payload with.

The provider returns a promise (see dojo/promise/Promise) that is fulfilled with the handled data of the response. The provider will also error out by calling the errorback function if provided. Progress data will be given to the progress handler if it is provided and if the platform supports progress events (any browser supporting XHR2 or node.js).

The promise returned by the provider has an extra property not on standard promises: response. This property is a standard promise that is fulfilled with an object representing the response from the server. This object will contain the following properties:

Property Description  
url The URL that was originally requested.
options Any options that were originally requested.
data Contains the data of the response if appropriate.
text Contains the text of the response if appropriate.
status Contains the status of the request as returned from the provider.
getHeaders(headerName) A function to retrieve headers sent from the server.

Examples

This example retrieves a resource from the server and then outputs the results that are returned.

require(["dojo/request", "dojo/dom", "dojo/dom-construct", "dojo/json", "dojo/on", "dojo/domReady!"],
function(request, dom, domConst, JSON, on){
  on(dom.byId("startButton"), "click", function(){
    domConst.place("<p>Requesting...</p>", "output");
    request("request/helloworld.json").then(function(text){
      domConst.place("<p>response: <code>" + text + "</code>", "output");
    });
  });
});
<h1>Output:</h1>
<div id="output"></div>
<button type="button" id="startButton">Start</button>

See also