Question

I have this script uses regular expressions to check that a form field contains a valid email address.Please explain me from declare

var emailfilter=/^\w+[\+\.\w-]*@([\w-]+\.)*\w+[\w-]*\.([a-z]{2,4}|\d+)$/i;

Thank you

Source:

<script type="text/javascript">

/***********************************************
* Email Validation script- © Dynamic Drive (www.dynamicdrive.com)
* This notice must stay intact for legal use.
* Visit http://www.dynamicdrive.com/ for full source code
***********************************************/

var emailfilter=/^\w+[\+\.\w-]*@([\w-]+\.)*\w+[\w-]*\.([a-z]{2,4}|\d+)$/i

function checkmail(e){
var returnval=emailfilter.test(e.value)
if (returnval==false){
alert("Please enter a valid email address.")
e.select()
}
return returnval
}

</script>

<form>
<input name="myemail" type="text" style="width: 270px"> <input type="submit" onClick="return checkmail(this.form.myemail)" value="Submit" />

</form>

Answer 1

/^\w+[\+\.\w-]*@([\w-]+\.)*\w+[\w-]*\.([a-z]{2,4}|\d+)$/i

/ = Begin an expression
^ = The matched string must begin here, and only begin here
\w = any word (letters, digits, underscores)
+ = match previous expression at least once, unlimited number of times
[] = match any character inside the brackets, but only match one
\+\. = match a literal + or .
\w = another word
- = match a literal -
* = match the previous expression zero or infinite times
@ = match a literal @ symbol
() = make everything inside the parentheses a group (and make them referencable)
[] = another character set
\w- = match any word or a literal -
+ = another 1 to infinity quantifier
\. = match another literal .
* = another 0 to infinity quantifier
\w+ = match a word at least once
[\w-]*\. = match a word or a dash at least zero times, followed by a literal .
() = another group
[a-z]{2,4} = match lowercase letters at least 2 times but no more than 4 times
| = “or” (does not match pipe)
\d+ = match at least 1 digit
$ = the end of the string
/ = end an expression
i = test the string in a case i nsensitive manner

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