Realm.List inherited functions seem missing in jest test

[peteroid]

Summary

When I was testing my model under Realm using Jest, it seems some functions were missing. For instance, map() and keys() would be missing and the test will throw the error saying TypeError: xxx.map is not a function. However, this error only happens in the jest but not in the normal execution.

After some trials, I found that replacing the map function from xxx.map(fn) to Realm.List.prototype.map.call(xxx, fn) could be working in both the jest test and normal execution.

Expected results

map function should be defined in the List object

Actual results

Jest threw errors like TypeError: xxx.map is not a function

Version

• realm: 1.3.1
• node: 7.10.0
• jest: 20.0.4

[John251314]

I met the same problem. what is the solution, in addition to the above method. Thanks.

[benweidig]

We ran into this exact issue today, but we needed some(...) which isn't
callable like that.

[kneth]

See also

• Libraries that use Symbol properties on builtin prototypes break in Jest jestjs/jest#4603
• Jest globals differ from Node globals jestjs/jest#2549

[visemet]

@kneth, I don't think this issue is specific to jest per-se though it is very much related to how jest uses vm.runInContext(). It appears that Realm.List instances do not have their prototype installed correctly when Realm is loaded from a separate context and are missing the properties from Realm.Collection.prototype.

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

function main() {
  const code = `
const Realm = require('realm');

const realm = new Realm({
  schema: [
    {
      name: 'PersonList',
      properties: {
        list: 'PersonObject[]',
      },
    },
    {
      name: 'PersonObject',
      properties: {
        name: 'string',
        age: 'double',
      },
    },
  ],
  deleteRealmIfMigrationNeeded: true,
});

realm.write(() => realm.deleteAll());

let object;
realm.write(() => {
  object = realm.create('PersonList', {list: [
    {name: 'Ari', age: 10},
    {name: 'Tim', age: 11},
    {name: 'Bjarne', age: 12},
  ]});
});

const methods = [];
let current = object.list;
do {
  methods.push(
    ...Object.getOwnPropertyNames(current).filter(prop => typeof object.list[prop] === 'function'));
} while ((current = Object.getPrototypeOf(current)));

realm.close();

new Set(methods);
`;

  const methodsInNewContext = vm.runInNewContext(code, {console, require});

  global.require = require;
  const methodsInThisContext = vm.runInThisContext(code);

  const difference = Array.from(
      new Set(
          [...methodsInThisContext].filter(x => !methodsInNewContext.has(x)))).sort();

  assert.deepStrictEqual(difference, []);
}

main();

AssertionError [ERR_ASSERTION]: Input A expected to strictly deep-equal input B:
+ expected - actual

- [
-   'concat',
-   'entries',
-   'every',
-   'filter',
-   'find',
-   'findIndex',
-   'forEach',
-   'join',
-   'keys',
-   'lastIndexOf',
-   'map',
-   'reduce',
-   'reduceRight',
-   'slice',
-   'some',
-   'values'
- ]
+ []

[kneth]

@kraenhansen You have a hypothesis why it isn't working, right?

[kraenhansen]

@kraenhansen You have a hypothesis why it isn't working, right?

I believed we have a similar issue with for(let ... of ...) loop on React Native. Originating from the way Realm JS is looping over the methods to export here: https://github.com/realm/realm-js/blob/master/lib/collection-methods.js#L49. I have a suspicion that some environments call the callback of forEach asynchronously.

But ... reading over the Jest issues, that you @kneth linked to, this does indeed seem like a known Jest bug. Perhaps a workaround could be found, but it seems more valuable to get the root cause fixed.

[takameyer]

@peteroid We took some time to try and reproduce this issue and failed to reproduce it. Can you try updating Jest and Realm, to see if the issue is resolved?

[takameyer]

The issues has been closed, as we are not able to reproduce it and no one in the community has reported that it is still an issue. If someone is seeing this issue, feel free to yell and we will reopen the issue.