Is that a real phone number? (British version).js

/*
Description:
Congratulations! That Special Someone has given you their phone number.

But WAIT, is it a valid number?

Your task is to write a function that verifies whether a given string contains a valid British mobile (cell) phone number or not.

If valid, return 'In with a chance'.

If invalid, or if you're given an empty string, return 'Plenty more fish in the sea'.

A number can be valid in the following ways:

Here in the UK mobile numbers begin with '07' followed by 9 other digits, e.g. '07454876120'.

Sometimes the number is preceded by the country code, the prefix '+44', which replaces the '0' in ‘07’, e.g. '+447454876120'.

And sometimes you will find numbers with dashes in-between digits or on either side, e.g. '+44--745---487-6120' or '-074-54-87-61-20-'. As you can see, dashes may be consecutive.

Good Luck Romeo/Juliette!
*/
function validateNumber(str){
  return /^(\+44|0|-0)?7(-*[0-9]){9}$/.test(str)?'In with a chance':'Plenty more fish in the sea'
}