How do i concat the values of select and input field and also display altogether with JavaScript

Question

I'm making a phone picker input menu which has a <select> and <input> field just like below:

<select id="country">
    <option data-countryCode="IN" value="91">India</option>
    <option data-countryCode="US" value="1">US</option>
    <option data-countryCode="GB" value="44">UK</option>
</select>

<input type="tel" placeholder ="956 826 4457" id="tel">

JS code:

 const select = document.querySelector('#country');
    const tel = document.getElementById('tel')
        tel.value = `${select.options[select.selectedIndex].value}` +`${tel.value}`

How do I concat/join the select value with the input field and also display whole together in that input field.

Answer 1

You can do something like this

const select = document.querySelector('#country');
const tel = document.getElementById('tel');
let prevVal = select.value; // storing previous value of select

// this block will be exected on init of code
if(tel.value) tel.value = `${select.value}${tel.value}`;
else tel.placeholder = `${select.value}${tel.placeholder}`;

// adding event on changing input
tel.addEventListener('change', ({ target }) => {
  const reg = new RegExp(`(^${prevVal} )`);
  // checking do we already have country code
  if (reg.test(target.value)) tel.value = tel.value.replace(reg, target.value);
  else tel.value = `${select.value}${target.value}`;
});

// adding event on changing select
select.addEventListener('change', ({ target }) => {
  const reg = new RegExp(`(^${prevVal})`);
  if(tel.value) tel.value = `${target.value}${tel.value.replace(reg, '')}`;
  else tel.placeholder =  tel.placeholder.replace(reg, target.value);
  prevVal = target.value;
});

<select id="country">
    <option data-countryCode="IN" value="91" selected>India</option>
    <option data-countryCode="US" value="1">US</option>
    <option data-countryCode="GB" value="44">UK</option>
</select>

<input type="tel" placeholder ="956 826 4457" id="tel">