Exchange Rates and Stock Quotes with YQL and jQuery

View Demo

Lately I was in need of a financial gadget that can provide stock exchange and currency data. I guess it goes without saying that you can find many solutions for the problem; in my case though none of them (that I found) was good enough to work with. I needed a free, reliable and highly customizable API. Unfortunately most of the free ones either come with an ugly copyright line which means a no go (why would you want to advertise your competition?), or they have some customization issues.

Since Google is no longer supporting it’s financial APIs (also it was a huge overkill compared to my simple needs) I found that Yahoo!’s Open Data Tables provides exactly what I want. It is well documented, easy-to-use, customizable and free (for my notes about reliability check out the last section of this post).

The code utilizes built-in ajax feature of jQuery. The URL of the request consists of three parts: the base url (http://query.yahooapis.com/v1/public/yql), the YQL query (you can read more about YQL here) and the configuration parameters (format=JSON etc.).

Query Processing

function YQLRequest( queryString, callback ){
  var url = "http://query.yahooapis.com/v1/public/yql?q=" + queryString +
         "&format=json&env=http://datatables.org/alltables.env&callback=?",
  jQuery.getJSON(url, callback);
}

Stock Quote

function getQuotes(){
  var q = escape( 'select * from yahoo.finance.quotes where symbol in ("AAPL","GOOG")' );
  YQLRequest( q, processQuotes );
}         

function processQuotes( data ){
  var quotes = data.query.results.quote;
  for( var i in quotes ) {
    // Do whatever you want with your data
    alert( quotes[i].Name + ' - ' + quotes[i].Ask + ' - ' + quotes[i].Bid );
  }
}

Exchange Rates

function getExchangeRates(){
  var q = escape( 'select * from yahoo.finance.xchange where pair in ("EURUSD","USDCAD")' );
  YQLRequest( q, processExchangeRates );
}         

function processExchangeRates( data ){
  var rates = data.query.results.rate;
  for( var i in rates ) {
    // Do whatever you want with your data
    alert( rates[i].Name + ' - ' + rates[i].Ask + ' - ' + rates[i].Bid );
  }
}

Reliability

While I was working on the script I had noticed some unexpected issues: null values and rejected requests. The latter one might be caused by the usage limit (1000 requests / hour / IP), but the problem was persistent even after an IP renewal. For this reason I implemented a cache which checks whether the response contains the expected values, if not, it serves the previous version from the cache.

To whom it may concern

When you work with YQL you might want to consider the following few rules and notes taken from the official site. You can find out more at the Yahoo! Developer Network.

Notice

• YQL can be used for commercial purposes
• If we’re going to shut down YQL, we will give you at least 6 months notice with an announcement on this web page and in our forum
• YQL has a performance uptime target of over 99.5%

Usage Limits

• Per application limit (identified by your Access Key): 100,000 calls per day
• Per IP limits: /v1/public/*: 1,000 calls per hour; /v1/yql/*: 10,000 calls per hour

Additional Notes

• All rates are subject to change
• You may also be subject to the underlying rate limits of other Yahoo! and 3rd party web services
• YQL relies on the correct operation of the web services and content providers it accesses

1st UPDATE

Since jQuery has introduced getJSON method I decided its time to refactor my code. This method is basically just a shortcode for an AJAX call optimized for JSON, but possible could save some bytes and improve readabilty.

2nd UPDATE

It turned out that Internet Explorer doesn’t want to play nicely with cross domain requests (thanks everyone for the feedbacks). To resolve the issue I appended the callback parameter to the URL to force jQuery to use JSONP instead of plain JSON. The new version should support IE from now on.