JS Validate Input

<input type='tel' data-filter='[0-9|+]*' placeholder='123+456'>
<input type='tel' data-filter='(\+|(\+[1-9])?[0-9]*)' placeholder='+10123'>
<input type='text' data-filter='([A-Z]?|[A-Z][a-z]*)' placeholder='Abcdefg'>
<input type='text' data-filter='([A-Z]{0,3}|[A-Z]{3}[0-9]*)' placeholder='ABC123'>

---

// Apply filter to all inputs with data-filter:
let inputs = document.querySelectorAll('input[data-filter]');

for (let input of inputs) {
  let state = {
    value: input.value,
    start: input.selectionStart,
    end: input.selectionEnd,
    pattern: RegExp('^' + input.dataset.filter + '$')
  };
  
  input.addEventListener('input', event => {
    if (state.pattern.test(input.value)) {
      state.value = input.value;
    } else {
      input.value = state.value;
      input.setSelectionRange(state.start, state.end);
    }
  });

  input.addEventListener('keydown', event => {
    state.start = input.selectionStart;
    state.end = input.selectionEnd;
  });
}