Consuming a public Rails API with jQuery

A previous post explained how to implement a public API in Rails. Here, we will cover how this API can be consumed with a cross-domain request using jQuery.

The idea

We’ll create a simple html file containing <ul> elements with an id. We’ll then use jQuery to fetch data (references and quantities) from the API provided by the Rails app we wrote in the previous post.


Very basic: we’ll just have a plain HTML page (with jQuery), and add <ul> elements for products:

<ul id="1">
<ul id="2">

The function

We’ll need to fetch the data form the remote API using JSONP, since we’ll be doing a cross-domain request to a remote server (even though everything is local; more on that here). So we’ll write a function that will take the id of the remote object we want information for:

function fetchProductData(id){
url: "http://localhost:3000/products/" + id + ".js",
dataType: "jsonp",
type: "GET",
processData: false,
contentType: "application/json",
success: function(data) {
$('#' + id).
append('<li>Remote id: ' + id + '</li>').
append('<li>Reference: ' + data['product']['reference'] + '</li>').
append('<li>Quantity: ' + data['product']['quantity'] + '</li>');

The setup for the function is relatively simple: pass in the API url, and some other parameters. One parameter you want to take special notice of is the “dataType: jsonp” which will make jQuery use JSONP to ensure the cross-domain request completes successfully (instead of returning an empty response). jQuery will transparently take care of specifying a callback and returning the wrapped data.

If and when the AJAX request completes successfully, we find the <ul> element to update, and add child <li> elements with the data. You’ll notice the data structure returned is pretty straightforward: the product model we defined in the previous post had a reference and a quantity, and they’re both returned in an a key-value fashion. (You can prevent the “product” root node from being included in the json data by setting ActiveRecord::Base.include_root_in_json = false in an initializer in your Rails 3 app.)

Updating every element on page load

First, we’ll define a function that will update every <ul> element on the page with a “product” class by fetching the appropriate data from the API:

function fetchData(){

Now, we simply have to call the “fetchData” function when the page has loaded:


If you now load the HTML document in a browser (while your Rails app is running), you’ll see the data being fetched from the “remote” server. Enjoy! (The full HTML file can be found here.)

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4 Responses to Consuming a public Rails API with jQuery

  1. Chris says:

    In rails 3.1.1, in wrap_parameters.rb, include_root_in_json is set to false by default. This will result in “TypeError: Result of expression ‘data['product']‘ [undefined] is not an object.” because it’s deleting the root element. The choice is either to set the value to true or to change the the function from data['product']['reference'] to data['reference'].

    Thanks for the awesome post, David. You saved another brain from melting.


  2. david says:

    Ah, I’m just starting to seriously look into the new functionality in Rails 3.1, and I haven’t had created any APIs with it yet. I personally prefer not having the root element included in the json…

    Thanks for the heads up, Chris !

  3. Usman Ahmed says:

    awesome tutorial.

    I’m trying to POST to rails API using jsonp, can you like do a little tutorial on that too?

  4. david says:

    It’s basically the same thing. But you (obviously) specify “POST” as the type. In addition, you need to add an attribute called “data”. For example: “data: {name: ‘John Doe’, age: 53},”. You can find more info about this at and ($.post is essentially shorthand for $.ajax with a type set to “POST”)