VirtualMV/JavaScript/Validation/Regular Expressions

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Regular Expressions are a good way of validating text fields. Basically, you create a string of characters that represents a validation and test it against a string. This approach compacts a lot of potentially confusing validation code down into a few lines.


In order to use a Regular Expression in JavaScript, you need to create a regex literal variable. So something like:

var myRegex = /^[a-z\s]+$/i;

The above says "do a case-insensitive check for alphabetical characters and spaces only".

/ - Start of a JavaScript regular expression
^ - Match the first character with the following
[a-z - Match the letters a through to z
\s] - Match spaces
+ - Use the previous rule for every character in the string
$ - Match the last character
/i - End of a JavaScript regular expression, and also sets the mode to case-insensitive

(Andersson, 2008)[1] gives an explanation of other patterns)

To test it against a string, we can use the "test" method that becomes available every time we create a variable containing a regular expression literal.

var rexLowerAlpha = /^[a-z\s]+$/i;
var strFail = "This test should fail!!!1111";
if (rexLowerAlpha.test(strFail)) {
  //do this if the test succeeds
} else {
  //do this if the test fails

The above is just for a match case, search and replace can also be done using regexs, as well as splitting strings up into arrays etc.

Alternatively you can create a string and then create a new regular expression object, for example:

    var rexStr1 = "^[a-z\s]+$/i;";
    var rexLowerAlpha = new RegExp(rexStr1);

Example jsRegExp_01.htm

There are heaps of pre-created regular expressions available here:

  • (2009)[2]

Useful patterns

Regular expressionWhat it does
/^[A-Z\s]+$/;Check for Uppercase A-Z plus space
/^[0-9]+$/;Check for integer e.g. 123,
/^(19|20)\d\d[- /.](0[1-9]|1[012])[- /.](0[1-9]|[12][0-9]|3[01])$/;matches a date in yyyy-mm-dd format from between 1900-01-01 and 2099-12-31, with a choice of four separators (-,/,space, and .) [3]

RegExp Tester

If you want to explore and experiment with Regular expressions you can do this in real time at


  • Contributors
    • ErinD Apr 2009

VmvIcon References.png References

  1. Andersson, D. (2008) Regular Expressions patterns. Retrieved June 8, 2009 from
  2. (2009) Regular Expression Library. Retrieved May 13, 2009 from
  3. Regular Expression Matching a Valid Date. Retrieved May 26, 2011 from
  4. (Chodnicki, S.(2011). An Introduction to Regular Expressions. Retrieved from
  5. RegExLibrary (2011) Dates and Times. Retrieved May 26, 2011 from

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VirtualMV/JavaScript/Validation/Regular Expressions. (2022). In WikiEducator/VirtualMV wiki. Retrieved August 12, 2022, from http:    (zotero)