Regular Expressions give you more power to validate strings in a script. With regular expressions you can create a pattern of what a valid value can be and test what was entered against it. For instance, you want to find out if a required field has data in it. Previous examples have shown how to check for an empty string or a space. However if two spaces were entered, the field would be valid. Look at the following pattern /^[ ]*$/.

• all patterns need to be surrounded by forward slashes "/"
• ^ match at the beginning of the field
• [ ] create a character set with a space in it
• * match the character preceding if it occurs zero or more times
• $ match at the end of the field
• in other words: check from the beginning of the field to the end of the field for all spaces

function isValidField(FirstName){
	var chkName = /^[ ]*$/; 
	if (chkName.test(FirstName)){
		alert("First Name cannot be blank");
		return false;
	}
	else
		return true;
}		

You want to find out if a valid email address has been entered. A normal email address has a combination of at least 3 characters and/or numbers before and after the "@" sign, followed by a ".". JavaScript string methods could be used to parse the information before and after the "@" and before the ".". This could be quite cumbersome.

/^[A-Za-z0-9]{2,}@[A-Za-z0-9_]{3,}\.[A-Za-z]{2}/ Look at the pattern to validate an email address.

• ^[A-Za-z0-9] this pattern says the first character can be any upper case letter A-Z or lower case letter a-z or a number 0-9.
• {2,} match the preceding patter for at least 2 or more characters
• @must contain a @ character
• [A-Za-z0-9_] the next character can be any upper case letter A-Z or lower case letter a-z or a number 0-9 or an underscore.
• {3,} match the preceding patter for at least 3 or more characters
• \.must contain a . character, since the dot is a special character it must be preceded by a backslash "\"
• [A-Za-z]the next character can be any upper case letter A-Z or lower case letter a-z
• {2}match the preceding patter for at least 2 characters

Validate a phone number (999) 999-9999. /(^[1-9][0-9]{2})([1-9][0-9]{2})([0-9]{4}$)/

• ^[1-9] the first character must be a number between 1-9.
• [0-9]{2} next two numbers must be between 0-9
• [1-9] the next number is between 1-9
• [0-9]{2} next two numbers must be between 0-9 .
• [0-9]{4}$ the last four numbers are between 0-9
• () notice the parentheses dividing the numbers into sections. The data is stored in memory so it can be used later. This can be used to put the data back together again

Remove Carriage Return and Line feed characters from a textarea. /\r\n/g

• /\r\n/ \r is a carriage return and \n is a line feed, we are looking for these two characters together.
• /\r\n/g adding a g after the expression means look for it globally.

Validate a phrase for alphanumeric characters (from the book). /[^a-z\d ]/i

• /[^a-z]/i match any character that is not between a-z, Note because there is a i to the end of the expression, the pattern is case insensitive. So match any character that is not between a-z and A-Z
• /[^a-z\d]/i match any character that is not between a-z, A-Z, or 0-9.
• /[^a-z\d ]/i match any character that is not between a-z, A-Z, 0-9, or a space.