A regular expression can easily check whether a user entered something that looks like a valid phone number.
Regular expressions are patterns used to match character combinations in strings.
Next, we use the is Na N() function to check if the phone number contain only numbers.
At last we check the length of the string and permit only phone numbers with 10 digits. When the user clicks the Submit button on the form, the form data is sent to a Java Script validation function that checks each field to make sure that it is in the appropriate format.
validate Phone ( ) The function below checks if the phone number is valid.
At first we use regular expression and the replace() method to clear out any spacer characters.
Also we will use trim() function that will trim leading whitespace off the string.
This wont be perfect validation it is possible to slip not compliant addresses by it but it's normally good enough.
You can use them to constrain input, apply formatting rules, and check lengths.