main.js

const button = document.querySelector('#button')
const input = document.querySelector('input')
const maskOptions = {
    mask: '(00) 00000-0000'
}

button.addEventListener('click', function (e) {
  e.preventDefault();
  let errorText = document.querySelector('#error');
  if(input.value == '') {
    errorText.innerHTML = 'Digite um número!';
    return
  }else {
    errorText.innerHTML = '';
  }
  const cellphoneNumber = input.value
  const formattedCellphoneNumber = cellphoneNumber.replace('(', '').replace(')', '').replace(' ', '').replace('-', '')
  const url = `https://api.whatsapp.com/send?phone=55${formattedCellphoneNumber}`
  window.open(url, '_blank').focus()
})

function configureMaskInput() {
  IMask(input, maskOptions)
}

configureMaskInput()