Synchronous loading of templates in a link tag.

rel-template.js

(function() {
  "use strict";

  Object.defineProperty(HTMLLinkElement.prototype, 'template', {
    get: function() {
      if(!/template/i.test(this.rel)) {
        return "";
      }

      var req = new XMLHttpRequest();
      req.open('GET', this.href, false);
      req.setRequestHeader('Accept', this.type || "*/*");
      req.send();

      if(req.status !== 200) {
        throw "Unable to retrieve the template.";
      } else {
        return req.responseText;
      }
    }
  });

})();

This would be perfect as a jQuery plugin like:

$('#body').render('myblog.html',data)

Where the render method could use your snippet to grab the template string and parse it with the data object, then attach the result to the element specified.

It would be perfect if it used the django/jinja template style of {% statement %} and {{ var | filter }}

This is template engine agnostic, intentionally. You can you any style you prefer, all this does is fetch the template from a link tag.