Add Concept Exercise for 'randomness': Captain's Log

[quintuple-mallard]

This PR adds hints.md,introduction.md, instructions.md, config.json, design.md, exemplar.js, captains-log.js, and captains-log.spec.js to a new exercise on the JavaScript track.

A couple of questions to a reviewer:

• The other exercises have these files:
  .gitignore, .npmrc, LICENSE, package.json, jest.config.js, global.d.ts, eslint.config.mjs, and babel.config.js. These are not mentioned in the docs though. Should I add these, or does that happen automatically somehow?
• How do I generate a UUID?

[github-actions]

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[Cool-Katt]

If you've used configlet, which is our tool for managing tracks and things like generating exercices, then all the needed files should be auto-generated and you shouldn't need to manually attach a UUID, but in case you do configlet can also do that.

Also worth checking out our (slightly outdated) CONTRIBUTING guide.

[Cool-Katt]

You probably want to use toMatch here.

[Cool-Katt]

I would have liked to see repeated testing like this in a for loop or something similar, so you can avoid repetition and we can test an arbitrary amount of times, because randomness is tricky.

Additionally, this - (41000<=randomStardate()<42000) is not valid JS syntax (technically it is but it doesn't work like in Python), because chained comparison isn't supported like that. You'll need something like (41000 <= stardate && stardate < 42000) instead.

[SleeplessByte]

I think this will work:

function loadDie(...values) {
  const originalRandom = Math.random()
  
  Math.random = function loadedDie { 
    if (values.length === 0) {
      return originalRandom();
    }
    
    return values.shift();
  }

  return () => {
    Math.random = originalRandom;
  }
}

describe('randomStardate',() => {
  test('stardate is between 41000 and 42000',() => {
    const restore = loadDie(
      0, 0, 0, 0, 0, 0,
      1, 1, 1, 1, 1, 1,
      0.5, 0.5, 0.5, 0.5, 0.5, 0.5
    );
    
    // 6 * 0, 6 * 1, 6 * 0.5 and everything else random
    
    for (let i = 0; i < 10_000; i++) {
      const starDate = randomStardate()
      expect(starDate).toBeGreaterThanOrEqual(41_000);
      expect(starDate).toBeLessThan(42_000);
    }
  
    restore();
  }
}

This should run in ~ 0.1 ms

[quintuple-mallard]

Errors in tests fixed, and for loops now used.

Just a question - is there a toInclude method?

[SleeplessByte]

(I wrote an entire thesis on how to calculate the expected number of rolls to get all the values in the planet class thing, but when I tried to submit it I pressed back accidentally and then lost it all. Will write it again soon...)

[SleeplessByte]

I think this will work:

function loadDie(...values) {
  const originalRandom = Math.random()
  
  Math.random = function loadedDie { 
    if (values.length === 0) {
      return originalRandom();
    }
    
    return values.shift();
  }

  return () => {
    Math.random = originalRandom;
  }
}

describe('randomStardate',() => {
  test('stardate is between 41000 and 42000',() => {
    const restore = loadDie(
      0, 0, 0, 0, 0, 0,
      1, 1, 1, 1, 1, 1,
      0.5, 0.5, 0.5, 0.5, 0.5, 0.5
    );
    
    // 6 * 0, 6 * 1, 6 * 0.5 and everything else random
    
    for (let i = 0; i < 10_000; i++) {
      const starDate = randomStardate()
      expect(starDate).toBeGreaterThanOrEqual(41_000);
      expect(starDate).toBeLessThan(42_000);
    }
  
    restore();
  }
}

This should run in ~ 0.1 ms

[SleeplessByte]

Just a question - is there a toInclude method?

Yes: toContain(item)

[SleeplessByte]

Okay. So I did this again.

In order to find out how many rolls we need to see each planet class in the following string:

'DHJKLMNRTY'

...we need to make a die that's fair with each side one class. There are 10 letters in the string. This math answer for a 6-sided die pointed me to terms to find this stats answer. We are looking for the 10 * harmonic(10) which is just shy of 30.

However, that gets us the average and we need to find out a reasonable number to use as maximum or at least a high probability (>95%, preferably >99.5%).

So I made this simulation in R.

Then I ran it 5 times:

29.2
   
Min. 1st Qu.  Median    Mean 3rd Qu.    Max. 
10.0    21.0    27.0    29.2    35.0   118.0 

29.2544

Min. 1st Qu.  Median    Mean 3rd Qu.    Max. 
10.00   21.00   27.00   29.25   35.00  131.00 

29.528

Min. 1st Qu.  Median    Mean 3rd Qu.    Max. 
10.00   21.00   27.00   29.53   35.00  118.00 

29.0984
Min. 1st Qu.  Median    Mean 3rd Qu.    Max. 
11.0    21.0    27.0    29.1    34.0   100.0 

29.53
Min. 1st Qu.  Median    Mean 3rd Qu.    Max. 
10.00   21.00   27.00   29.53   35.00   93.00 

This tells me that the average number is spot on, and that we can use 200 rolls to get all the values, but to make it completely improbable that a correct solution yields an incomplete set, we can do it 1_000 times.

describe('randomPlanetClass', () => {
  test('planet classes are valid',  () => {
    const expected = 'DHJKLMNRTY'
    const seen = {}

    for (let i=0; i < 1_000; i++){
      const actual = randomPlanetClass()
      expect(expected).toContain(actual)
    }
  })

  test('all planet classes can be returned',  () => {
    const expected = 'DHJKLMNRTY'
    const seen = {}

    for (let i=0; i < 1_000; i++){
      const actual = randomPlanetClass()
      seen[actual] = true
    }

    expected(Object.keys(seen).length).toBe(expected.length);
  })
    
  // remove the other test, it's no longer necessary
})

[quintuple-mallard]

Tests updated and uuid added.

[Cool-Katt]

@quintuple-mallard You can run lint and format actions locally on your end. Might be easier than waiting for an approval for the workflow to run

[quintuple-mallard]

@quintuple-mallard You can run lint and format actions locally on your end. Might be easier than waiting for an approval for the workflow to run

I am trying this, but it is saying 'missing file'. Should I change the directory?

[Cool-Katt]

It's explained in more detail in the contributing guide that I linked earlier, but it would look something like this (when ran from root)

corepack pnpm node scripts/lint.mjs

[quintuple-mallard]

It's explained in more detail in the contributing guide that I linked earlier, but it would look something like this (when ran from root)

corepack pnpm node scripts/lint.mjs

How do I get to the root directory? I am quite new to CLIs and configlet