Mask US phone number string with JavaScript

Question

I need regular express for US Phone Number format.I want to replace the phone number string into below US phone number string format in JavaScript.

var number = "4031234789";

And I want to mask it in below format:-

number = number.mask('[phone]');

Can anyone show me a regular expression for that in JavaScript?

Answer 1

This answer assumes you want the following format: [phone] (as the OP states).

^{There are multiple different ways to implement this, but here are a couple different approaches:}

---

If you want to simply mask the number on the blur event (when the field loses focus), then you could use the following:

document.getElementById('phone').addEventListener('blur', function (e) {
  var x = e.target.value.replace(/\D/g, '').match(/(\d{3})(\d{3})(\d{4})/);
  e.target.value = '(' + x[1] + ') ' + x[2] + '-' + x[3];
});

<p>Masked on the blur event (remove focus).</p>
<input type="text" id="phone" placeholder="[phone]"/>

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Alternatively, if you would rather mask the number while typing, you can listen to the input event and then conditionally mask the number based on the regex match:

document.getElementById('phone').addEventListener('input', function (e) {
  var x = e.target.value.replace(/\D/g, '').match(/(\d{0,3})(\d{0,3})(\d{0,4})/);
  e.target.value = !x[2] ? x[1] : '(' + x[1] + ') ' + x[2] + (x[3] ? '-' + x[3] : '');
});

<input type="text" id="phone" placeholder="[phone]"/>