Functional programming in JS is possible, ramda / wu (others?) make it very easy to get started, of course it is not as great as with functional programming languages, but still, it allows you to do pretty cool stuff, it's like lodash but with the callback moved to the first argument, turning something like this:

var isMultilanguage = function(field) {

  return field.multilanguage === true;

};

var isNotMultilanguage = function(field) {

  return field.multilanguage !== true;

};

var getMultilanguageFields = function (fields) {

  return _.filter(fields, isMultilanguage); 

};

var getNonMultilanguageFields = function (fields) {

  return _.filter(fields, isNotMultilanguage); 

};

into this

var isMultilanguage = R.where({multilanguage: true});

var isNotMultilanguage = R.not(isMultilanguage);

var getMultilanguageFields = R.filter(isMultilanguage);

var getNonMultilanguageFields = R.filter(isNotMultilanguage);

https://github.com/ramda/ramda

https://github.com/fitzgen/wu.js