Javascript string.replace with regex

Question

I want to replace a url querystring parameter with a new value if it already exists or add it on if not.

e.g.

The current url could be:
a. www.mysite.com/whatever.asp?page=5&version=1 OR
b. www.mysite.com/whatever.asp?version=1

I need the resulting url to be www.mysite.com/whatever.asp?page=1&version=1

I suspect I can use string.replace with a regex to do this the most intelligent way but am hoping for a little help with it from someone more experienced with regexs :) Thanks!

jAndy · Accepted Answer · 2011-02-22 07:43:13Z

2

I would rather use location.search along with some .splits() and Array.prototype.some^help.

var s     = location.search.slice(1).split(/&/);
    check = s.some(function(elem) {
        return elem.split(/=/)[0] === 'page';
    });

if(!check) s.push('page=1');

location.href = location.hostname + location.pathname + '?' + s.join('&');

answered Feb 22, 2011 at 7:43

jAndy

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Jimbo Over a year ago

Thanks for your answer. I gave it to Benson as I used his to solve my problem and for the lesson in regexs :P

Benson · Accepted Answer · 2011-02-22 07:43:42Z

0

I think the clearest solution would be to write one regex that parses the URL, and then build a URL from there. Here's what I would do:

function urlCleanup(url) {
  var match = /http:\/\/www\.mysite\.com\/whatever.asp\?(page=(\d+))?&?(version=(\d+))?/.exec(url);
  var page = match[2] ? match[2] : "0";
  var version = match[4] ? match[4] : "0";
  return "http://www.mysite.com/whatever.asp?page=" + page + "&version=" + version;
}

var testUrls = [ "http://www.mysite.com/whatever.asp?page=4"
               , "http://www.mysite.com/whatever.asp?version=5"
               , "http://www.mysite.com/whatever.asp?page=4&version=5" ];

for(i in testUrls)
  console.log(urlCleanup(testUrls[i]));

One problem this doesn't handle is having the variables in the opposite order in the url (e.g. ?version=5&page=2). To handle that, it would probably make more sense to use two regexes to search the URL for each parameter, like this:

function urlCleanup(url) {
  var match, page, version;
  match = /version=(\d+)/.exec(url);
  version = match ? match[1] : "0";
  match = /page=(\d+)/.exec(url);
  page = match ? match[1] : "0";

  return "http://www.mysite.com/whatever.asp?page=" + page + "&version=" + version;
}

var testUrls = [ "http://www.mysite.com/whatever.asp?page=4"
               , "http://www.mysite.com/whatever.asp?version=5"
               , "http://www.mysite.com/whatever.asp?version=5&page=2"
               , "http://www.mysite.com/whatever.asp?page=4&version=5" ];

for(i in testUrls)
  console.log(urlCleanup(testUrls[i]));

edited Feb 22, 2011 at 7:43

answered Feb 22, 2011 at 7:30

Benson

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5 Comments

Jimbo Over a year ago

Max respect :P Let me play with it for a bit now :)

Benson Over a year ago

I'm playing with what I wrote here in a console, and it's not quite right, I'll edit in a much cleaner version shortly.

Jimbo Over a year ago

Its actually only the page part that I need to play with. If page parameter exists, replace it with new one, otherwise add it to the end

Benson Over a year ago

Oh, crap. My answer is far too complex for what you need then, sorry I misread the question. For that, you just need a subset of my second code block -- let me know if it's not obvious what you need to do.

Jimbo Over a year ago

This helped me solve the problem by using your regex examples, thanks a lot.

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