regex for telephone number in validation form

Question

in a django template with the html pattern tag and boostrap for form validation

with this regex it validates a sequence of numbers that can be separated by a dash

"^[+-]?\d(?:-?\d)+$"

example:

12-65-25-75-84 or 12-255-0214

the javascript:

(() => {
    'use strict'    
    const forms = document.querySelectorAll('.needs-validation')
    
    Array.from(forms).forEach(form => {
        form.addEventListener('submit', event => {
            if (!form.checkValidity()) {
                event.preventDefault()
                event.stopPropagation()
            }

            form.classList.add('was-validated')
        }, false)
    })
})()

and the html

<input type="text" class="form-control" id="exampleFormControlInput1" name="tel" id="tel" placeholder="Tel" pattern="^[+-]?\d(?:-?\d)+$" required>
                            </div>

I would like to know how to modify it to have the possibility of putting spaces between the numbers (in addition to the dashes)

example:

12 57 125-98-457

and limit the total number of digits to 15 (excluding spaces and dashes)

for example a string like this:

12-28-35-74-12

or

12 28 35 74 12

or 123-478 25 12 124-15

thank you

Answer 1

I would use:

^[0-9](?:[ -]?[0-9]){0,14}$

See RegEx Demo

1. ^ - Matches the start of the string.
2. [0-9] - Matches a single digit (0, 1, ... 9).
3. (?: - Start of a non-capturing group.
4. [ -]? - Optionally matches either a space or '-'.
5. [0-9] - Matches a single digit (0, 1, ... 9).
6. ) - End of the non-capturing group.
7. {0,14} - Maches the previous token, ie the previous non-capturing group, from 0 to 14 times.
8. $ - Matches the end of the string.