mongoose-extract-duplicate-field/index.js

Extracts duplicate key name from Mongoose error with code 11000.

'use strict';
var assert = require('assert');

module.exports = function (error) {

  assert(error, 'error cannot be undefined');
  assert(error.code, 'error.code cannot be undefined');
  assert(error.code === 11000, 'error should be a duplicate key error with code 11000');
  assert(error.message, 'error.message cannot be undefined');

  try {
    var field = error.message.split('.$')[1];
    field = field.split(' dup key')[0];
    field = field.substring(0, field.lastIndexOf('_'));
    return field;
  } catch (e) {
    throw new Error('could not parse error.message');
  }
};