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dojo.io.script

Status:Contributed, Draft
Version:1.0
Available:since V0.9

Introduction

This is an alternate IO mechanism to dojo.xhrGet that has the capability of doing cross-site data access. It accomplishes this feat by doing an IO call via a dynamically inserted <SCRIPT> tag into your web page.

JSONP

Aside from being able to do cross-site data access, this implementation provides support for JSONP which is a way callback names can be added to a script return and executed appropriately. Not all services that provide script-tag data formats support JSONP, but many do and it makes it very flexible.

Limitations

  • The dojo.io.script package can only make requests that are effectively ‘GET’ style requests with query parameters. It does not support any other HTTP verb, such as POST, PUT, and DELETE.
  • Since dojo.io.script relies on dynamic script tags, it cannot be done in a synchronous fashion (unlike dojo.xhrGet). Therefore, any usage of this function must be async aware and async safe.

Usage

To make an IO call using a script tag (for instance, for cross-domain JSONP calls), dojo.require(“dojo.io.script”), and use:

  • dojo.io.script.get() with a JavaScript Object parameter. The JavaScript object supports the following properties:

dojo.io.script.get() supported object properties

url The URL to request data from.
callbackParamName The URL parameter name that indicates the JSONP callback string. For instance, when using Yahoo JSONP calls it is normally callbackParamName: “c”.
checkString A string of JavaScript that when evaluated like so: “typeof(” + checkString + “) != ‘undefined’” being true means that the script fetched has been loaded. Do not use this if doing a JSONP type of call (use callbackParamName instead).
preventCache

A boolean value that tells dojo.xhrGet to append a unique query parameter to each request. The purpose of this parameter is to keep the browser from caching the results. While it is generally good practice to let the server tell your browser how to cache and when to clear, sometimes it is necessary to force the browser to not cache.

This parameter is optional

content

A JavaScript object of name/string value pairs. These items are converted to query parameters and passed on as part of the url. Example request made by the browser: <url>?key1=value1&key2=value2&key3=value3..

This parameter is optional

Note: “handleAs” is NOT applicable to dojo.io.script.get() calls, since it is implied by the usage of “callbackParamName” (response will be a JSONP call returning JSON) or “checkString” (response is pure JavaScript defined in the body of the script that was attached).

Examples

Example 1: dojo.io.script call to fetch data from the Google Search API (JSONP)

<script>
 dojo.require("dojo.io.script");

  function searchGoogle() {
    //Look up the node we'll stick the text under.
    var targetNode = dojo.byId("results");

    //The parameters to pass to xhrGet, the url, how to handle it, and the callbacks.
    var jsonpArgs = {
      url: "http://ajax.googleapis.com/ajax/services/search/web",
      callbackParamName: "callback",
      content: {
        v: "1.0",
        q: "dojo toolkit"
      },
      load: function(data){
        //Set the data from the search into the viewbox in nicely formatted JSON
        targetNode.innerHTML = "<pre>" + dojo.toJson(data, true) + "</pre>";
      },
      error: function(error){
        targetNode.innerHTML = "An unexpected error occurred: " + error;
      }
    };
    dojo.io.script.get(jsonpArgs);
  }
  dojo.addOnLoad(searchGoogle);
</script>
<b>Google Search Results for 'dojo toolkit' (In JSON):</b>
<div id="results" style="height: 200px;"></div>