Form Validation and Regular Expressions

Q. What if we want to test for a string pattern other than "null" or "empty"?...
A. Regular Expressions!

Simplified Regular Expression for an email address:

/^[\w\._-]+@[\w\._-]+\.[a-zA-Z]{2,7}$/

^
beginning of the string
[\w\._-]+
[square brackets] indicate a character class
"\w" is a word character
"+" means 1 or more times
@
the "@" part of the email address
\.[a-zA-Z]{2,7}
matches the TLD (dot something, where something is 2 to 7 letters
$
end of string
Example 8.9 - Form Validation with Regular Expressions - Example 8.9 | JavaScript example9.js

 <form onsubmit="return Validate(this)" method="get" action="https://cscis12.dce.harvard.edu/echo">
   <div>
     <label for="email1">Email Address     </label>:
     <input type="text" size="32" name="email" id="email1"/>

     <br/>

     <input type="submit"/>

   </div>
 </form>

In head element: 

<script src="example9.js"> </script>

Contents of example9.js


/* validates that the entry is formatted as an email address */
function Validate(thisForm) {
    let tocheck = thisForm.email.value;
    let re = /^[\w\._-]+@[\w\._-]+\.[a-zA-Z]{2,7}$/;
    if (!tocheck.match(re)) {
        alert("Please verify the email address format.");
        thisForm.email.focus();
        thisForm.email.style.backgroundColor = '#ff9';
        return false;
    } else {
        return true;
    }
}
 

js form validatoin