 Sample Usage
Now that you’ve been introduced to regular expressions
and patterns, let’s look at a few examples of common validation and
formatting functions.
- Valid Number
A valid number value should contain only an optional
minus sign, followed by digits, followed by an optional dot (.) to signal
decimals, and if it's present, additional digits. A regular expression to
do that would look like this:
var anum=/(^-*\d+$)|(^-*\d+\.\d+$)/
- Valid Date Format
A valid short date should consist of a 2-digit month,
date separator, 2-digit day, date separator, and a 4-digit year (e.g.
02/02/2000). It would be nice to allow the user to use any valid date
separator character that your backend database supported such as slashes,
dashes and periods. You want to be sure the user enters the same date
separator character for all occurrences. The following function returns
true or false depending on whether the user input matches this date
format:
function checkdateformat(userinput){
var dateformat = /^\d{1,2}(\-|\/|\.)\d{1,2}\1\d{4}$/
return dateformat.test(userinput) //returns true or false depending on userinput
}
This example uses backreferencing to ensure that the
second date separator matches the first one.
- Replace HTML tags (brackets) with entities instead
User input often times must be parsed for security or to
ensure it doesn't mess up the formatting of the page. The most common task
is to remove any HTML tags (brackets) entered by the user, and replace
them with their entities equivalent instead. The following function does
just that- replace "<" and ">" with "<" and ">", respectively:
function htmltoentity(userinput){
var formatted=userinput.replace(/(<)|(>)/g,
function(thematch){if (thematch=="<") return "<"; else return ">"})
}
The first parameter of replace() searches for a match for either
"<" or ">". The second parameter demonstrates something new and
interesting- you can actually use a function instead of a plain
replacement text as the parameter. When a function is used, the parameter
of it (in this case, "thematch") contains the matched substring and
returns what you wish it to be replaced with. Since we're looking to
replace both "<" and ">", this function will help us return two different
replacement strings accordingly.
And with that this tutorial concludes. As you can see, Regular
Expressions really isn't that difficult to understand, with a little time
and practice that is!
This tutorial is written by
Karen Gayda. Modified by
JavaScriptKit.com for structure and added additional content plus
examples. Karen Gayda is a Senior Software Engineer in the Internet
Services Division at Stellcom Technologies located in San Diego, CA.
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