Question

I wish to request data from a web service endpoint( say “http://www.example.com“) using javascript.

After retrieving it , there will be a callback function to process the response ( which will be a JSON object )

How do I go about writing it? A skeleton code will do.

Will it be something like:

<script>

function callback(data)
{
    // the response text would be processed here.
}
       url="http://www.example.com";
       var script = document.createElement('script');
       script.src = url;
       script.onload=callback;
       document.body.appendChild(script);        
</script>

Thanks in advance.

Answer 1

As noted by @JuicyScripter in the comment above…

“Wikimedia API which Wikipedia use supports JSONP callback argument.”

This means that you can add a callback to the query…

var url = "http://en.wikipedia.org/w/api.php?action=query&prop=info|revisions&intoken=edit&titles=Main%20Page&format=json&callback=my_callback";

Notice at the end I added &callback=my_callback. What will happen is that instead of sending a JSON response like…

{
    query: {
        pages: {
            15580374: {
                ...
            }
        }
    }
}

…it will now be wrapped in a function call. This will be valid JavaScript, so your script request will execute the function, and pass the data.

my_callback({
    query: {
        pages: {
            15580374: {
                ...
            }
        }
    }
});

So all you need is a callback function that has the same name as the function you gave in the query…

function my_callback( data ) {
    console.log( data );
}

Make sure this function is globally available.

Then get rid of the onload line, and your code should just work…

var url = "http://en.wikipedia.org/w/api.php?action=query&prop=info|revisions&intoken=edit&titles=Main%20Page&format=json&callback=my_callback";
var script = document.createElement('script');
script.src = url;
document.body.appendChild(script);     

When the script arrives and runs, it will invoke your function passing it the data requested.