Question

The underscore template documentation suggest the following should be possible, yet it is not working for me. Executing the template simply returns nothing for this.

<% FB.api('/me', function(response){ %>
<%= response.name %>
<% }); %>

Answer 1

That’s a perfectly valid template; in fact, the compiled JavaScript version looks like this (reformatted for readability):

function(obj) {
    var __p = '';
    var print = function() { __p += Array.prototype.join.call(arguments, '') };
    with(obj || {}) {
        __p += '\n';
        FB.api('/me', function(response) { 
            __p += '\n' + response.name + '\n';
        }); 
        __p += '\n';
    }
    return __p;
}

And there’s nothing wrong with that. BTW, you can look at the source attribute of a compiled Underscore template if you want to see the JavaScript for the template:

var t = _.template(raw_template);
console.log(t.source);

However, it won’t do what you’re expecting it to do. Your problem is that the FB.api call is an AJAX call and A stands for asynchronous. So by the time your callback gets called (i.e. <%= response.name %> is executed), the template will have been converted to HTML and added to the DOM and nothing will be looking at the __p variable anymore. The sequence looks something like this:

1. Compile the template and call the compiled template function.
2. FB.api gets called.
3. The template function returns some HTML.
4. The HTML from 3 is added to the DOM.
5. Time passes.
6. Facebook responds and your FB.api callback gets called.
7. response.name is appended to the __p buffer.

You’re going to have to turn your logic inside out a bit. Your FB.api call should be outside your template:

var t = _.template(...);
FB.api('/mu', function(response) {
    var html = t({ response: response });
    // Somehow add html to the DOM
});

so that you don’t try to use the template until all the data is ready.