Question

Is there a Javascript templating library that automatically infers the variables used in the template and the possible dependencies among them? If I for example have a template that looks like this (Handlebars syntax):

<script id="entry-template" type="text/x-handlebars-template">
<div class="entry">
  <h1>{{title}}</h1>
  <div class="body">
    {{body}}
  </div>
</div>
</script>

I would like to be able to do something like this:

var source   = $("#entry-template").html();
var template = Handlebars.compile(source);
template.vars() => {title: "", body: ""}

The reason I would like this functionality is that I would like to be able to generate a form with fields reflecting the variables needed to complete the template.

Answer 1

This snippet (edit at http://jsfiddle.net/CfaAW/2/) uses a Regex to find the simple {{var}} syntax, and will also look for . to handle Handlebars Paths.

function extractObjectFromTemplate(source) {
    var handlebarsRegex = /\{\{([\s\S]+?)\}\}/g;
    var varObject = {};
    var varArray, ns, o, i, len;
    while ((varArray = handlebarsRegex.exec(source)) !== null) {
        ns = varArray[1].split('.');
        o = varObject;
        for (i = 0, len = ns.length; i < len; i++) {
            o = o[ns[i]] = o[ns[i]] || (i == len - 1 ? "" : {});
        }
    }

    return varObject;
}

On your template, a JSON.stringify(extractObjectFromTemplate(source)) gives you this:

{"title":"","body":""}

and with Handlebars Paths in your template

<h1>{{title.h1}}</h1>
<h2>{{title.h2}}</h2>
<div class="body">
  {{body}}
</div>

you will get the nested properties

{"title":{"h1":"","h2":""},"body":""}