What is the correct way to do .has(), .get() and .set() for javascript Map() used in an ExpressJS server?

Question

javascript Map() has thrown me off. My question is about javascript Map() - set, get and has(). I thought I was an expert on it, but apparently not...

Situation: I have a 'global' map - a map saved on a different .js file that gets 'required'. This map's keys are the _id of MongoDB documents. The values of this map are class objects of node-schedule - an npm package. The value part can be ignored since my problem is with .get(), .has() and .set()

Here is my method that (fails to) cancel jobs:

    cancelJob: async function (id) {
        console.log('---- inside cancelJob ---');
        console.log('id = ', id);
        console.log('map = ', config.map);
        console.log('map size = ', config.map.size);
        if (config.map.has(id)) {
            console.log('---- map has id ---');
            let job = config.map.get(id);
            console.log('job = ', job);
            await job.cancel();
            config.map.delete(id);
            console.log('---- deleted 1 from map ---');
        }
    },

The if statement always returns false. I previously tried the .get() and checked if the returned value is not undefined, but it was undefined. let me share the console log of my server - resulting from the above code, after I do .set() and (failed to do) .delete() a couple of times:

id =  5f9c3b171a5d1b26089d60fe
map =  Map {
  5f9c3b171a5d1b26089d60fe => Job {
    job: [Function],
    callback: false,
    name: '<Anonymous Job 1>',
    trackInvocation: [Function],
    stopTrackingInvocation: [Function],
    triggeredJobs: [Function],
    setTriggeredJobs: [Function],
    cancel: [Function],
    cancelNext: [Function],
    reschedule: [Function],
    nextInvocation: [Function],
    pendingInvocations: [Function]
  },
  5f9c3b171a5d1b26089d60fe => Job {
    job: [Function],
    callback: false,
    name: '<Anonymous Job 2>',
    trackInvocation: [Function],
    stopTrackingInvocation: [Function],
    triggeredJobs: [Function],
    setTriggeredJobs: [Function],
    cancel: [Function],
    cancelNext: [Function],
    reschedule: [Function],
    nextInvocation: [Function],
    pendingInvocations: [Function]
  }
}
map size =  2

As you can see, map doesn't store (!?) the values to the same key slot? I am confused. I thought I learned that keys are unique, and that it should find the key... Please help me figure this out if you can :)

PS: I did ctrl + F on the ID value, and it turns out the ID string is the same for all the keys and the ID parameter.

Edit 1: Here is the method that sets the map:

convertDocumentToScheduledJob: function (dbJob) {
 // prepare date and rule here...
 let j = schedule.scheduleJob(dbJob.recurrence == 'no-recurrence' ? date : rule, function () {
            // does stuff
        })
        config.map.set(dbJob._id, j);
}

I am using this convertDocumentToScheduledJob method to set/insert map key-value pairs. This whole thing is part of a full-stack web app, so there are multiple controllers that call these 2 methods, but I'm pretty sure those don't directly affect anything here. They just invoke these 2 methods.

Again, as seen in my PS message above, when I console log the config.map, it shows 2 map entries with the same keys. ~~Isn't that worrying?~~

Edit 2: @FelixKling solved this problem. The key was of data type, Object. I had to convert that to String to resolve this. Thank you.

    console.log('Type of job_id = ', typeof dbJob._id);
    let strId = JSON.stringify(dbJob._id);
    console.log('Type of strID = ', typeof strId);
    config.map.set(strId, j);

Key's are unique in a map, there is something missing here, can you show the code were your filling the map. — Keith, Nov 02 '20 at 15:12
Sure. Here is the code that sets the map: ```javascript convertDocumentToScheduledJob: function (dbJob) { let j = schedule.scheduleJob(dbJob.recurrence == 'no-recurrence' ? date : rule, function () { // does stuff }) config.map.set(dbJob._id, j); ``` — Tenzin Thabkhae, Nov 02 '20 at 15:16
@FelixKling nice catch. Turns out the typeof dbJob._id is `object`. Although it should have been a string. This is a major breakthrough. Thanks. Edit: dbJob is a MongoDB document. — Tenzin Thabkhae, Nov 02 '20 at 15:35
*"... it shows 2 map entries with the same keys. Isn't that worrying?"* Since it's not possible that a map has two entries with the same keys, the only conclusion can be that the keys must be different, which would be the case with a string object for example. But `dbJob._id` might be any object that possibly implements `toString`. — Felix Kling, Nov 02 '20 at 15:37
Thank you. I updated my code to resolve this problem. It's very reasonable to check the data type of the map key and not to take a MongoDB string value to have the string datatype as granted. — Tenzin Thabkhae, Nov 02 '20 at 15:44

score 0 · Accepted Answer · answered Nov 03 '20 at 22:13

@FelixKling solved this question in the comments.

The key was of data type Object. I had to convert that to String to resolve this. Thank you.

Solution 1 (incomplete):

console.log('Type of job_id = ', typeof dbJob._id);
let strId = JSON.stringify(dbJob._id);
console.log('Type of strID = ', typeof strId);
config.map.set(strId, j);

This eliminates the duplicated key bug. New map entries now properly replace the old map entry with the same key.
The problem still persists when I invoke cancelJob(id) where the id is a basic string value. JSON.stringified string is different from regular string. (it has an extra double quote)
MongoDB documentation shows a way to convert ._id to regular string via the .toString() method. [Sources: StackOverFlow source; MongoDB Documentation]

Solution 2:

    convertDocumentToScheduledJob: function (dbJob) {
        // ...
        let strId = dbJob._id.toString();
    },
    cancelJob: async function (raw_id) {
        // ...
        let id = typeof raw_id == 'object' ? raw_id.toString() : raw_id;
    },

What is the correct way to do .has(), .get() and .set() for javascript Map() used in an ExpressJS server?

1 Answers1