Friday, April 19, 2024

How to Use a JavaScript Query String Parser


In this article you’ll learn how to obtain and use the data from the
query string portion of the URL by using a JavaScript query string
parser. Without a JavaScript query string parser, the query string data
is accessible only to CGI scripts. Thus, this script is especially
useful for people whose Web sites are served by free hosting
providers. For most of these millions of people, there’s no access to
custom CGI capability, so a JavaScript query string parser is the only
way to make multifunction Web pages.

Using a JavaScript query string parser is one of my favorite
techniques. I’ve used it for online photo galleries, tracking coupon
codes, writing online order forms, creating some of the original
browser-based Rich Text editors and many other things.

A JavaScript query string parser has a place even for those with
access to CGI programming, .NET frameworks, PHP, SQL, etc. It’s so
versatile that it can easily do things that CGI can’t do. Since learning JavaScript in 1999, I’ve needed to write
HTML programs which run on a client’s computer without any CGI
programming or Web server software. Without a JavaScript query string parser I’d have no way to do this.

Background Information

A Uniform Resource Locator (URL) provides a “method for finding”
something. As an example, if you accessed the Internet directly, then would be a URL as well as a URI (uniform
resource identifier). If you accessed the Internet through a proxy,
then the URI would be, but perhaps the URL
would be It’s rarely
necessary to distinguish between URI and URL, but URL has become
ubiquitous. However, in some technical writing, URI is preferred.

The most powerful part of a URL for a Web developer is its query
string. The query string contains data values and parameters from a
form or other programs which submit data to your Web site.

It’s important for all Web developers to have access to the query
string data contained in a URL. This is especially true for
developers who can’t afford to pay for their own Web sites. The content
at a free Web site is NOT necessarily inferior to the content at a
registered domain name. Sometimes it’s the other way around. Many people enjoy free Web hosts like Angelfire, as evidenced
by Angelfire’s ranking of 620 out of billions of Web sites.

Format of the query string

An HTTP URL is defined in RFC 2616 (HTTP/1.1) by:

Perhaps you’ve noticed that long and garbled looking URLs look
normal at first, and have wondered whether someone went crazy after the
question mark. Before the question mark is simply the Web host and the
complete path name of the file being accessed, relative to the server
or virtual host document root. After the question mark is the data
being communicated, called the “query” or the “query string.”

The query string is usually logged in the server log files*, but
unless a program is there to handle the query, and understands what was
in it, nothing much will happen. You can even submit data of your own.
Thankfully, so far as I know, it isn’t yet illegal to submit random
data for the purposes of experimentation.

(Using static files rather than CGI scripts and recording the data
in a log file for future processing is efficient bulk data
processing for high traffic Web sites. You can imagine, “Your request
will be processed within the next five minutes.” Running one program to
process 500 little lines of a log file every five minutes is an idea
that I’ve taken advantage of to improve the performance of a Web server
struggling to launch several new CGI scripts every second.)

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