javascript email regular expression

Question

Can someone explain this regular expression to validate email.

var emailExp = /^[\w\-\.\+]+\@[a-zA-Z0-9\.\-]+\.[a-zA-z0-9]{2,4}$/;

I need to know what does this independent elements do

"/^" and "\" and "\.\-" and "$" //Please explain individually

Thanks in advance

• KJYe.Name: regular-expressions.info/reference.html
• Quentin: That expression is broken and will reject many perfectly valid email addresses.
• Brad Mace: possible duplicate of What is the best regular expression for validating email addresses?

Answer 1

Quick explanation

/

JavaScript regular expressions start with a / and end with another one. Everything in-between is a regular expression. After the second / there may be switches like g (global) and/or i (ignore case) ie. var rx = /.+/gi;)

^

Start of a text line (so nothing can be prepended before the email address). This also comes in handy in multi-line texts.

\

Used to escape special characters. A dot/full-stop . is a special character and represents any single character but when presented as \. it means a dot/full-stop itself. Characters that need to escaped are usually used in regular expression syntax. (braces, curly braces, square brackets etc.) You'll know when you learn the syntax.

\.\-

Two escaped characters. Dot/full-stop and a minus/hyphen. So it means .-

$

End of line.

Learn regular expressions

They are one of the imperative things every developer should understand to some extent. At least some basic knowledge is mandatory.

Some resources

• General regular expression syntax resource
  http://www.regular-expressions.info/
• JavaScript related regular expressions
  https://developer.mozilla.org/en/Core_JavaScript_1.5_Guide/Regular_Expressions

• Some Java Guy: @Robert: So my regex to allow a hyphen in the middle of the number would look like this ? var numericExpression_and_hyphen_in_middle = /^[0-9]+\-[0-9]+$/
• Robert Koritnik: @oneofthelions: This will force a hyphen, not allow it. If you'd like to allow it, it should be followed by a question mark: /^[0-9]+-?[0-9]+$/. And it also doesn't mean that it will be right in the middle. At least one digit will be proceeding it and at least one succeeding. But there may not be equal number of digits on each side.
• Some Java Guy: @Robert: That is what I want to force the hyphen in middle. Now if I want at least one character after hyphen and at two would look like this?/^[0-9]+\-[0-9]{1,2}+$/
• Robert Koritnik: @oneofthelions: Oh and BTW: A hyphen doesn't need to be escaped as long as it's not part of a range definition in a set as in [0-9]. But even there it can be used freely when it can't make a conflict as in [0-9a-z.+-] All of these in a set are meant as literals.
• Robert Koritnik: @oneofthelions: Almost. Remove the trailing + at the end. As long as you want these characters to be digits and not any characters. /^[0-9]+-?[0-9]{1,2}$/. AND if you do talk about digits, these two are equal: [0-9] = \d. So it can be shortened to: /^\d+-?\d{1,2}$/

Answer 2

/

The start of the expression

^

The start of the string (since it appears at the start of the expression)

\

Nothing outside the context of the character that follows it

\.\-

A full stop. A hyphen.

$

The end of the string

Answer 3

The other posters have done an excellent job at explaining this regex, but if your goal is to actually do e-mail validation in JavaScript, please check out this StackOverflow thread.