Replace Specified Part of QueryString With JavaScript

I need a function which will replace a given part of a querystring. The function needs to look like this:

function replaceQueryStringPart(url, name, value) {
    ...
}

It needs to work as follows:

replaceQueryStringPart('http://localhost/test.asp?name=brian&phone=12345', 'name', 'fred') //Returns http://localhost/test.asp?name=fred&phone=12345

replaceQueryStringPart('http://localhost/test.asp?name=brian&phone=12345', 'phone', '67890') //Returns http://localhost/test.asp?name=brian&phone=67890

If the specified querystring part does not exist, it must be appended to the end of the querystring as follows:

replaceQueryStringPart('http://localhost/test.asp?name=brian&phone=12345', 'email', 'test@server.com') //Returns http://localhost/test.asp?name=brian&phone=67890&email=test@server.com

replaceQueryStringPart('http://localhost/test.asp', 'email', 'test@server.com') //Returns http://localhost/test.asp?email=test@server.com

I have spent a few hours on this now and realised I need to use the JavaScript RegExp object with the replace method, but I can't get my head around regular expressions enough to write the function. Would be very grateful for any assistance.

-William
LVL 1
wwarbyAsked:
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ZvonkoSystems architectCommented:
I used a small trick, but what do you think of this:

<script>
function replaceQueryStringPart(theUrl, theParam, theValue){
   theUrl = theUrl.replace(new RegExp("[\\?\\&]?"+theParam+"\\=[^\\&]+","i"),"");
   if(theUrl.indexOf("?")>-1){
     return theUrl+"&"+theParam+"="+theValue
   } else {
     return theUrl+"?"+theParam+"="+theValue
   }
}

alert(replaceQueryStringPart('http://localhost/test.asp?name=brian&phone=12345', 'name', 'fred'));
alert(replaceQueryStringPart('http://localhost/test.asp?name=brian&phone=12345', 'phone', '67890'));
alert(replaceQueryStringPart('http://localhost/test.asp?name=brian&phone=12345', 'email', 'test@server.com'));
alert(replaceQueryStringPart('http://localhost/test.asp', 'email', 'test@server.com'));
</script>



0
wwarbyAuthor Commented:
It's almost there, except the first alert box returns 'http://localhost/test.asp&phone=12345?name=fred', which isn't correct syntax. I'll have a look at what you've done and see if I can fix it myself - if you have any suggestions I'd be really grateful. Other than that, it's exactly what I wanted. These regular expressions seem like an impenetrable encrypted language to me - I've read three tutorials and am no closer to understanding them.

-William
0
ZvonkoSystems architectCommented:
Uhps sorry. I did not test it well.

Here the revised version:
<script>
function replaceQueryStringPart(theUrl, theParam, theValue){
   theUrl = theUrl.replace(new RegExp("\\&?"+theParam+"\\=[^\\&]+","i"),"");
   theUrl = theUrl.replace("?&","?");
   if(theUrl.indexOf("?")>-1){
     return theUrl+"&"+theParam+"="+theValue
   } else {
     return theUrl+"?"+theParam+"="+theValue
   }
}

alert(replaceQueryStringPart('http://localhost/test.asp?name=brian&phone=12345', 'name', 'fred'));
alert(replaceQueryStringPart('http://localhost/test.asp?name=brian&phone=12345', 'phone', '67890'));
alert(replaceQueryStringPart('http://localhost/test.asp?name=brian&phone=12345', 'email', 'test@server.com'));
alert(replaceQueryStringPart('http://localhost/test.asp', 'email', 'test@server.com'));
</script>


The problem with upper RegExp is that it has to be expressed as string and that is additionaly confusing because of doubled back slashes.
The basic expression is this:  
 String.replace(/\&?parm\=[^\&]+/, "")

And that expression matches this:
   \&?   : zero or one & character
   param\=    : matches that string "param="
  [^\&]+   : matches all characters until the next & character.

So the matched upper characters are replaced by empty string (they are removed from the URL)
The additional String.replace("?@", "?")  does only a paramter shift is the removed paramter was the first parameter (Uhps now I see next problem and will be back in a second...)




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ZvonkoSystems architectCommented:
Ok, I got it.
This is more robust:
<script>
function replaceQueryStringPart(theUrl, theParam, theValue){
   theUrl = theUrl.replace(new RegExp("([\\?\\&]"+theParam+"\\=)[^\\&]+","i"),"$1"+theValue);
   if(theUrl.indexOf("?")<0) return theUrl+"?"+theParam+"="+theValue
   if(theUrl.indexOf(theParam+"=")<0) return theUrl+"&"+theParam+"="+theValue
   return theUrl;
}

alert(replaceQueryStringPart('http://localhost/test.asp?name=brian&phone=12345', 'name', 'fred'));
alert(replaceQueryStringPart('http://localhost/test.asp?name=brian&phone=12345', 'phone', '67890'));
alert(replaceQueryStringPart('http://localhost/test.asp?name=brian&phone=12345', 'email', 'test@server.com'));
alert(replaceQueryStringPart('http://localhost/test.asp?email=some@server.com', 'email', 'test@server.com'));
alert(replaceQueryStringPart('http://localhost/test.asp', 'email', 'test@server.com'));
</script>

The additional $1 parameter in the replacing string is the matching content from the first braces match group.

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wwarbyAuthor Commented:
Thanks very much ;-)

Your last one seems to work fine, although I think I may have cracked it myself from your first reply - here's my solution:

<script>
    function replaceQueryStringPart(theUrl, theParam, theValue){
        if (theUrl.indexOf('?' + theParam)>-1) {
            theUrl = theUrl.replace(new RegExp('\\??'+theParam+'\\=[^\\&]+','gi'),'?'+theParam+'='+theValue);
        } else if (theUrl.indexOf('&' + theParam)>-1) {
            theUrl = theUrl.replace(new RegExp('\\&?'+theParam+'\\=[^\\&]+','gi'),'&'+theParam+'='+theValue);
        } else {
            if (theUrl.indexOf("?")>-1) {
                return theUrl+"&"+theParam+"="+theValue
            } else {
                return theUrl+"?"+theParam+"="+theValue
            }
        }
        return theUrl
    }

alert(replaceQueryStringPart('http://localhost/test.asp?name=brian&phone=12345&email=test@server.com', 'name', 'fred'));
alert(replaceQueryStringPart('http://localhost/test.asp?name=brian&phone=12345&email=test@server.com', 'phone', '67890'));
alert(replaceQueryStringPart('http://localhost/test.asp?name=brian&phone=12345&email=test@server.com', 'email', 'foo@bar.com'));
alert(replaceQueryStringPart('http://localhost/test.asp', 'fax', '34567'));
</script>

Certainly couldn't have done it without your example ;-)

-William
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ZvonkoSystems architectCommented:
Thanks for points.
And you are right, go for your solution. That is the only real way!

See you,
Zvonko

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