isCheckbox() — Basic | @andresclua/validate

import { isCheckbox } from '@andresclua/validate'

const checkboxes = document.querySelectorAll('.c--form-checkbox-a__item')
const config = { minRequired: 1 }

// On Change
checkboxes.forEach(cb => {
    cb.addEventListener('change', () => {
        const result = isCheckbox({ elements: checkboxes, config })
        errorEl.textContent = result.isValid ? '' : result.errorMessage
    })
})

// On Submit
validateBtn.addEventListener('click', () => {
    const result = isCheckbox({ elements: checkboxes, config })
    errorEl.textContent = result.isValid ? '' : result.errorMessage
})

<div class="c--form-group-a">
  <div class="c--form-checkbox-a">
    <input type="checkbox" id="item-1" class="c--form-checkbox-a__item">
    <label class="c--form-checkbox-a__title" for="item-1">JavaScript</label>
  </div>
  <div class="c--form-checkbox-a">
    <input type="checkbox" id="item-2" class="c--form-checkbox-a__item">
    <label class="c--form-checkbox-a__title" for="item-2">CSS</label>
  </div>
  <span class="c--form-error-a"></span>
</div>

/* Orientative — feel free to adapt to your own conventions */

.c--form-group-a {
    margin-bottom: 1.5em;
}

.c--form-checkbox-a {
    display: flex;
    align-items: center;
    gap: 8px;
    margin-bottom: 0.5em;
}

.c--form-checkbox-a__item {
    width: 16px;
    height: 16px;
    cursor: pointer;
    accent-color: currentColor;
}

.c--form-checkbox-a__title {
    font-size: 1em;
    cursor: pointer;
}

.c--form-error-a {
    color: red;
    font-size: 0.875em;
    display: none;
}
.c--form-error-a:not(:empty) { display: block; }

minRequired  number  Minimum number of checkboxes required to be checked. Default: 1