How to add context helper to Dust.js base on server and client

Question

How to add context helper to Dust.js base on server and client

I'm working with Dust.js and Node/Express. Dust.js documents the context helpers functions, where the helper is embedded in the model data as a function. I am adding such a function in my JSON data model at the server, but the JSON response to the browser doesn't have the function property (i.e. from the below model, prop1 and prop2 are returned but the helper property is not.

/* JSON data */
model: {
    prop1: "somestring",
    prop2: "someotherstring",
    helper: function (chunk, context, bodies) {
        /* I help, then return a chunk */
    }
/* more JSON data */

I see that JSON.stringify (called from response.json()) is removing the function property. Not sure I can avoid using JSON.stringify so will need an alternative method of sharing this helper function between server/client. There probably is a way to add the helper functions to the dust base on both server and client. That's what I'm looking for. Since the Dust docs are sparse, this is not documented. Also, I can't find any code snippets that demonstrate this.

Thanks for any help.

node.js
dust.js

Answer 1

send your helpers in a separate file - define them in a base context in dust like so:

base = dust.makeBase({foo:function(){ code goes here }})

then everytime you call your templates, do something like this:

dust.render("index", base.push({baz: "bar"}), function(err, out) {
  console.log(out);
});

what this basically does is it merges your template's context into base, which is like the 'global' context. don't worry too much about mucking up base if you push too much - everytime you push, base recreates a new context with the context you supplied AND the global context - the helpers and whatever variables you defined when you called makeBase.

hope this helps

Answer 2

If you want stringify to preserve functions you can use the following code.

JSON.stringify(model, function (key, value) {
  if (typeof(value) === 'function') {
    return value.toString();
  } else {
    return value;
  }
});

This probably doesn't do what you want though. You most likely need to redefine the function on the client or use a technology like nowjs.