I have this template script
You can use ajax to load the template file.
With jQuery:
$.get("user_template.js", function(template_text){
var template = Handlebars.compile(template_text);
// more things
});
I would use RequireJS for this. Lovely to work with modules and there is also a plugin that is called text that works beautifully with templates.
If it sounds interesting, here's some links:
http://requirejs.org/
http://requirejs.org/docs/download.html#text -- The text plugin
RequireJS is only suitable if you want to use modules though, if not Alon's answer is better.