npm install mongoose-error-helper

var errorHelper = require('mongoose-error-helper').errorHelper;


function (req, res, next) {
    //generate `user` here
    user.save(function (err) {
        //If we have an error, call the helper, return, and pass it `next`
        //to pass the "user-friendly" errors to
        if (err) return errorHelper(err, next);
    }
}

{ message: 'Validation failed',
  name: 'ValidationError',
  errors:
   { username:
      { message: 'Validator "required" failed for path username',
        name: 'ValidatorError',
        path: 'username',
        type: 'required' },
     state:
      { message: 'Validator "enum" failed for path state',
        name: 'ValidatorError',
        path: 'state',
        type: 'enum' },
     email:
      { message: 'Validator "custom validator here" failed for path email',
        name: 'ValidatorError',
        path: 'email',
        type: 'custom validator here' },
     age:
      { message: 'Validator "min" failed for path age',
        name: 'ValidatorError',
        path: 'age',
        type: 'min' } } }

[ 'username is required.',
  'state not an allowed value.',
  'custom validator here',
  'age below minimum.' ]