tpl3d.js proof of concept

mapping.js

var flatObj = {
  simple_str: 'simple',
  stringified_array: 'simple,array',
  'a.1': 'item first',
  'a.0': 'item second'
  'obj.field': '1.0'
};

var treeTemplate = {
  unstringified: [
    'stringified_array',
    function (value) {
      value.split(',');
    }
  ],
  aa: /a\.\d+/,
  ab: [
    /a\.\d+/,
    null,
    function (key) {
      return key.split('.')[1];
    }
  ]
  obj: {
    field_original: 'obj.field',
    field_scalar: [
      'obj.field',
      function (value) {
        parseInt(value);
      }
    ]
  }
};

// the same with router-like API
var marshal = function (m) {

  m.cmap('stringified_array', m.toJSON, 'unstringified');
  m.mmap('a', function (key, self) { // it will be a out-of-the-box helpers for this
    var r = {}, i;
    for (i in self.aa) {
      r[key + '.' + i] = self.aa[i];
    }
    return r;
  });
  m.map('obj.field', ['obj', 'field_orig']);

};


var treeObj = //flat2tree(flatObj, treeTemplate);
{
  simple_str: 'simple', // as is
  unstringified: ['simple', 'array'],
  aa: ['item second', 'item first'], // in order of sorted keys
  ab: {
    '1': 'item first',
    '0': 'item second'
  },
  obj: {
    field_original: '1.0',
    field_scalar: 1
  }
};

var flatTemplate = {
  stringified_array: [
    'unstringified',
    function (value) {
      return value.join(',');
    }
  ],
  a: 'ab', // most unclear momnent
  'obj.field': [
    null,
    function (self) {
      return self.obj.field_original;
    }
  ]
};

// the same with router-like API
var unmarshal = function (u) {

  u.map('simple_str'); // redundant, it's a default
  u.map('simple_str', 'copy_of_simple_str');

  u.cmap('stringified_array', u.fromJSON, 'unstringified');

  u.amap(/a\.\d+/, 'aa');
  u.map(/a\.\d+/, function (k) {
    return ['ab', k.split('.')[1]];
  });

  u.map('obj.field', ['obj', 'field_orig']);
  u.cmap('obj.field', u.scalar, ['obj', 'field_scalar']);

  u.tcmap(/obj\..+/, parseInt, '.');
};

var result = // tree2flat(treeObj, treeTemplate);
{
  simple_str: 'simple',
  stringified_array: 'simple,array',
  'a.1': 'item first',
  'a.0': 'item second'
  'obj.field': '1.0'
};