validators ignore undefined (as documented)

output.txt

ohnob@DESKTOP-A4G2C0J MSYS ~/repos/mongoose-validators-hard-to-use
$ node --version
v6.11.1

ohnob@DESKTOP-A4G2C0J MSYS ~/repos/mongoose-validators-hard-to-use
$ npm list mongoose
[email protected] C:\Users\ohnob\repos\mongoose-validators-hard-to-use
`-- [email protected]  extraneous

npm ERR! extraneous: [email protected] C:\Users\ohnob\repos\mongoose-validators-hard-to-use\node_modules\mongoose

ohnob@DESKTOP-A4G2C0J MSYS ~/repos/mongoose-validators-hard-to-use
$ node validators-ignore-undefined.js

assert.js:81
  throw new assert.AssertionError({
  ^
AssertionError: undefined == true
    at Object.<anonymous> (C:\Users\ohnob\repos\mongoose-validators-hard-to-use\validators-ignore-undefined.js:23:8)
    at Module._compile (module.js:570:32)
    at Object.Module._extensions..js (module.js:579:10)
    at Module.load (module.js:487:32)
    at tryModuleLoad (module.js:446:12)
    at Function.Module._load (module.js:438:3)
    at Module.runMain (module.js:604:10)
    at run (bootstrap_node.js:389:7)
    at startup (bootstrap_node.js:149:9)
    at bootstrap_node.js:504:3

validators-ignore-undefined.js

const assert = require('assert');
const mongoose = require('mongoose');

const ThingSchema = new mongoose.Schema({
  // https://stackoverflow.com/a/44336895/429091, doesn’t support
  // subdocuments.
  undefinedDisallowed: {
    type: String,
    valiate: {
      validator: function (v) {
        return v !== undefined;
      },
    },
    default: null,
  },
});

const Thing = mongoose.model('Thing', ThingSchema);

const thing = new Thing();
assert.ifError(thing.validateSync());
thing.undefinedDisallowed = undefined;
assert.ok(thing.validateSync());