Generate array with values A1, A2, A3, B1, B2, B3... etc?

Question

I'm trying to generate an array of objects where it outputs an array looking like this:

[
    {
      _id: 2,
      label: 'A1'
    },
    {
      _id: 3,
      label: 'A2'
    },
    {
      _id: 4,
      label: 'A3'
    },
    {
      _id: 5,
      label: 'B1'
    },
    {
      _id: 6,
      label: 'B2'
    },
    {
      _id: 7,
      label: 'B3'
    }
  ]

And all the way up to letter "G"... However, I cant quite to seem to wrap my head around how to generate this automatically. So far I've come up with this, but in my output it's skipping letters, and just isn't generating correctly :) Could use some help on this.

What I have so far:

function nextChar(c) {
   return String.fromCharCode(c.charCodeAt(0) + 1);
}

const supersetOptions = computed(() => {
  const maxGroup = 6;
  const maxItems = 12;
  let defaultLetter = 'a';

  return Array.from({ length: maxItems }, (value, index) => {
    const currentLetter = nextChar(defaultLetter)
    defaultLetter = nextChar(currentLetter);
    return {
      label: `${currentLetter}${index + 1}`,
      value: `${currentLetter}${index + 1}`
    };
  });
})

Answer 1

You appear to start the _id from 2, but I've assumed this is a typo. If not, then just i+2 instead of i+1 on line 8.

You also have different property names between what you say you want, and what your code is attempting to produce. This matches what you said you wanted.

function generate(count) {
    const results = []

    for(let i = 0 ; i < count ; i++) {
        const letter = String.fromCharCode(65 + (i / 3))
        const delta = (i % 3) + 1
        results.push({
            _id: i+1,
            label: `${letter}${delta}`
        })
    }

    return results
}

console.log(generate(21))

Answer 2

You could increment the letter after the wanted group size and check with remainder.

const
    nextChar = c => (parseInt(c, 36) + 1).toString(36),
    computed = () => {
        const
           maxPerGroup = 3,
           maxItems = 12;

        let letter = 'a';

        return Array.from({ length: maxItems }, (_, index) => {               
            const value = `${letter}${index % maxPerGroup + 1}`;
            index++;
            if (index % maxPerGroup === 0) letter = nextChar(letter);
            return { index, value };
        });
    }

console.log(computed());

.as-console-wrapper { max-height: 100% !important; top: 0; }

Answer 3

Using generator

function* labels(end) {
  for (let i = 0; i <= end; i += 1) {
    yield {
      _id: i + 1,
      label: `${String.fromCharCode(65 + (Math.floor(i / 3) % 26))}${i % 3 + 1}`
    }
  }
}

for (const item of labels(122)) {
  console.log([item._id, item.label])
}