Unknown Template Variables

[dominicporteous]

Is there a way to preserve the templated variable if a variable is undefined in the compile context?

e.g.

Hi, Hello {{ name }}! Its a {{ mood }} day.

Compiled with the following context;

{name: "Dom"}

Would result in the following output;

Hi, Hello Dom! Its a {{ mood }} day.

I've had a look through the api, and even some of the code, but I cant seem to find what I'm looking for.

The mustache docs state the following;

By default a variable "miss" returns an empty string. This can usually be configured in your Mustache library. The Ruby version of Mustache supports raising an exception in this situation, for instance.

http://mustache.github.io/mustache.5.html

I cant seem to find the place to configure this in Handlebars. Any help would be much appreciated!

[mcintyre94]

If your variables are flat (no nesting), then this workaround works:

// If a variable x is missing, put {{x}} in, ie retain it as a variable
handlebars.registerHelper('helperMissing', function({ name }) {
    return new handlebars.SafeString(`{{${name}}}`);
});

When your template is compiled with that context, it'll call helperMissing({name: 'mood', ...}) automatically (see http://handlebarsjs.com/builtin_helpers.html#helperMissing), so that implementation just returns it {{mood}} for that case.

Note that it only works with top-level variables though, so if you had {{user.name}} and {{weather.mood}} that wouldn't work unfortunately.

[EricMCornelius]

@dominicporteous @mcintyre94 Just ran into this issue as well. I've got a workaround (HACK) to handle arbitrary nesting via ES6 Proxy objects for the interim:

const hbs = require('handlebars');

const handler = path => ({
  get(target, prop, receiver) {
    if (typeof prop !== 'string') return;

    const toString = () => `{{{${path}}}}`;
    if (prop === 'toString') return toString;
    if (prop === 'toJSON') return toString;
    if (prop === 'toHTML') return toString;

    const full_path = path !== '' ? `${path}.${prop}` : prop;
    const new_target = target[prop];

    if (new_target === undefined) return context_proxy({}, full_path);
    if (typeof new_target === 'object') return context_proxy(new_target, full_path);
    return new_target;
  }
});

const context_proxy = (obj, path = '') => new Proxy(obj, handler(path));

const template_ = hbs.compile('Hi, Hello {{ data.name }}! Its a {{ data.mood }} day.');
const context = context_proxy({
  data: {
    name: 'Eric'
  }
});

const res = template_(context);

console.log(res);

Hi, Hello Eric! Its a {{{data.mood}}} day.

[nknapp]

Closing due to inactivity, but this may be related to #1435

[hkurra]

@dominicporteous @mcintyre94 Just ran into this issue as well. I've got a workaround (HACK) to handle arbitrary nesting via ES6 Proxy objects for the interim:

const hbs = require('handlebars');

const handler = path => ({
  get(target, prop, receiver) {
    if (typeof prop !== 'string') return;

    const toString = () => `{{{${path}}}}`;
    if (prop === 'toString') return toString;
    if (prop === 'toJSON') return toString;
    if (prop === 'toHTML') return toString;

    const full_path = path !== '' ? `${path}.${prop}` : prop;
    const new_target = target[prop];

    if (new_target === undefined) return context_proxy({}, full_path);
    if (typeof new_target === 'object') return context_proxy(new_target, full_path);
    return new_target;
  }
});

const context_proxy = (obj, path = '') => new Proxy(obj, handler(path));

const template_ = hbs.compile('Hi, Hello {{ data.name }}! Its a {{ data.mood }} day.');
const context = context_proxy({
  data: {
    name: 'Eric'
  }
});

const res = template_(context);

console.log(res);

Hi, Hello Eric! Its a {{{data.mood}}} day.

It is really good solution, thanks for providing this solution.
how to handle block level Helper like {{#each}}?
blockHelperMissing hooks works only if name matches a property in the current evaluation context.