How to compose a regular expression with only one + at the beginning, and then only numbers?

Question

JavaScript

form.addEventListener('input', evt => {
  const target = evt.target;
  if (target.name === 'user_phone') {
    target.value = target.value.replace(/123/, '');
  }
});

We need a regular expression that leaves only the first "+" and subsequent digits in the replace method (and there may not be a +).

Answer 1

.replace(/^[^+\d]*(\+|\d)|\D/g, '$1');