Restafarian "code-on-demand" example used to inform client what a valid resource is, including non-authorative property validations.

description.js

Function.prototype.curry = function() {
  var fn    = this;
  var slice = Array.prototype.slice;
  var args  = slice.call(arguments);

  return function() {
    return fn.apply(this, args.concat(slice.call(arguments)));
  }
}

var Resource = {};
 
Resource.name =  "User";

Resource.flags = {
  create: 1,
  update: 2,
  save:   1 | 2,
}

Resource.validators = {
  base: function(opts, fn, errors, key, on) {
    if(on & (opts.on || Resource.flags.save)) {
      key = fn.call(this, key, opts);
      if(key) {
        errors[key] = errors[key] || [];
        errors[key].push(opts.message);
      }
    };
  },
  
  presence: function(opts) {
    return this.base.curry(opts, function(key, _) {
      if(!this[key]) return key;
    });
  },
  
  length: function(opts) {
    return this.base.curry(opts, function(key, opts) {
      var string = this[key] || "";
      var l   = opts.tokenizer(string).length;
      var min = opts.minimum;
      var max = opts.maximum;
      
      if(l < min || l > max) return key;
    });
  },
  
  acceptance: function(opts) {
    return this.presence(opts);
  },
  
  inclusion: function(opts) {
    return this.base.curry(opts, function(key, opts) {
      if(opts['in'].indexOf(this[key]) < 0) return key;
    });
  },
  
  confirmation: function(opts) {
    return this.base.curry(opts,function(key, _) {
      if(this[key] !== this[key + '_confirmation']) {
        return key + '_confirmation';
      }
    });
  }
}

Resource.validate =  function(representation, on) {
  var errors = {};
  for(var property in this.properties) {
    if(this.properties.hasOwnProperty(property)) {
      this.properties[property].validators.forEach(function(validator) {
        validator.call(representation, errors, property, on);
      })
    }
  };
  return errors;
}

Resource.properties = {
  full_name: {
    localized_name: "Full name",
    type: "text",
    validators: [Resource.validators.presence({'message': 'must be present'}),
                 Resource.validators.length({'message': "is too short", "minimum": 2, "tokenizer": function(string) { return string.split(/\W+/);  }}),
                 Resource.validators.inclusion({'message': 'must be one of the flower pot men', 'in': ['Bill', 'Bob']})]
  }
}

// var errors = Resource.validate({ "full_name" : "Bob" }, Resource.flags.save);
//
// { full_name: ["is too short", "must be one of the flower pot men"]