sprintf url formatting in javascript - php

Question

how do i write a function in javascript that can get the current url eg:
http://www.blahblah.com/apps/category.php?pg=1&catId=3021
and depending on a user selection choice, appends another parameter to the url like:
http://localhost/buyamonline/apps/category.php?pg=1&catId=3021&limit=5
but heres the catch:
Everytime the user selects a diff choice, I dont want to keep appending stuff like
http://localhost/buyamonline/apps/category.php?pg=1&catId=3021&limit=5&limit=10 and so on.
I want to always replace add it if there is no limit parameter or replace the value if there is one.
I was trying to accomplish this using sprintf but failed.
i was doing like so:
var w = document.mylimit.limiter.selectedIndex;
var url_add = document.mylimit.limiter.options[w].value;
var loc = window.location.href;
window.location.href = sprintf(loc+"%s="+%s, "&limit", url_add);

Answer 1

Updated with regular expression solution implemented in JS.
You can use a regular expression using JavaScript replace() Method
You can use build the entire url each time rather than just appending a parameter
You can parse the url into it's parts before appending the parameter
Which would you prefer?
For #1: The following should do the trick. Note though, there are issues with using regular expressions for parsing urls. (Ref: stackoverflow.com/questions/1842681/…)
<script type="text/javascript">
var pattern = "&limit(\=[^&]*)?(?=&|$)|^foo(\=[^&]*)?(&|$)";
var modifiers = "";
var txt=new RegExp(pattern,modifiers);
var str="http://localhost/buyamonline/apps/category.php?pg=1&catId=3021&limit=5";
document.write(str+"<br/>");
var replacement = "&limit=10";
document.write(str.replace(txt, replacement));
</script>

Answer 2

Below you can find my sprintf implementation which you can use it in your JS code to achieve what you need. It works almost like the C++/Java/PHP sprintf function with some limitations: the format specifiers are written like %1 and does not support the typed format specifiers (like %d, %s, %.2f, etc).
String.prototype.sprintf = function() {
var matches,result = this, p = /%(\d)/g;
while (matches = p.exec(result)) {
result = result.replace(matches[0], arguments[parseInt(matches[1]) - 1]);
}
return result;
};
Syntax:
format.sprintf(arg1,arg2,...);
The format string is composed of zero or more format specifiers that follows this prototype:
a % followed by argument index, where the first argument has index 1.
The arg1, arg2, ... are the variable strings which will replace the format specifiers.
Example: 'The quick %1 fox jumps over the %2 dog'.sprintf('brown','lazy');
Usage example:
var str = 'The size of %1 (%2) exceeds the %3 (%4).';
console.log(str.sprintf('myfile.txt', '100MB', 'max. allowed size', '75MB'));
Output:
The size of myfile.txt (100MB) exceeds the max. allowed size (75MB).
Note: If you need a robust sprintf function then check the sprintf for JavaScript.