Partial matching a string against a regex

Question

Suppose that I have this regular expression: /abcd/ Suppose that I wanna check the user input against that regex and disallow entering invalid characters in the input. When user

Answer 1

I think that you have to have 2 regex one for typing /a?b?c?d?/ and one for testing at end while paste or leaving input /abcd/

This will test for valid phone number:

const input = document.getElementById('input')

let oldVal = ''
input.addEventListener('keyup', e => {
  if (/^\d{0,3}-?\d{0,3}-?\d{0,3}$/.test(e.target.value)){
    oldVal = e.target.value
  } else {
    e.target.value = oldVal
  }
})
input.addEventListener('blur', e => {
  console.log(/^\d{3}-?\d{3}-?\d{3}-?$/.test(e.target.value) ? 'valid' : 'not valid')
})

And this is case for name surname

const input = document.getElementById('input')

let oldVal = ''
input.addEventListener('keyup', e => {
  if (/^[A-Z]?[a-z]*\s*[A-Z]?[a-z]*$/.test(e.target.value)){
    oldVal = e.target.value
  } else {
    e.target.value = oldVal
  }
})
input.addEventListener('blur', e => {
  console.log(/^[A-Z][a-z]+\s+[A-Z][a-z]+$/.test(e.target.value) ? 'valid' : 'not valid')
})