Add or update query string parameter

pQuery.js

// Add / Update a key-value pair in the URL query parameters
function updateUrlParameter(uri, key, value) {
    // remove the hash part before operating on the uri
    var i = uri.indexOf('#');
    var hash = i === -1 ? ''  : uri.substr(i);
         uri = i === -1 ? uri : uri.substr(0, i);

    var re = new RegExp("([?&])" + key + "=.*?(&|$)", "i");
    var separator = uri.indexOf('?') !== -1 ? "&" : "?";
    if (uri.match(re)) {
        uri = uri.replace(re, '$1' + key + "=" + value + '$2');
    } else {
        uri = uri + separator + key + "=" + value;
    }
    return uri + hash;  // finally append the hash as well
}

Nice work @niyazpk and @amorgner - quite helpful!

Update to amorgner's code to allow setting falsy values.

I wanted to be able to set 0 and similar "falsy" values in the URL so I have modified it so only remove a value if null is specifically passed in.

Otherwise anything that evaluated to false would unset, which wasnt he behaviour I wanted.

Tweaked code: https://gist.github.com/niyazpk/f8ac616f181f6042d1e0#gistcomment-1743025

Thanks all to those improving this, pass it on 👍

function updateUrlParameter(uri, key, value) {
    // remove the hash part before operating on the uri
    var i = uri.indexOf('#');
    var hash = i === -1 ? ''  : uri.substr(i);
    uri = i === -1 ? uri : uri.substr(0, i);

    var re = new RegExp("([?&])" + key + "=.*?(&|$)", "i");
    var separator = uri.indexOf('?') !== -1 ? "&" : "?";

    if (value === null) {
        // remove key-value pair if value is specifically null
        uri = uri.replace(new RegExp("([?&]?)" + key + "=[^&]*", "i"), '');
        if (uri.slice(-1) === '?') {
            uri = uri.slice(0, -1);
        }
        // replace first occurrence of & by ? if no ? is present
        if (uri.indexOf('?') === -1) uri = uri.replace(/&/, '?');
    } else if (uri.match(re)) {
        uri = uri.replace(re, '$1' + key + "=" + value + '$2');
    } else {
        uri = uri + separator + key + "=" + value;
    }
    return uri + hash;
}

Typescript version

Tweaked code: https://gist.github.com/niyazpk/f8ac616f181f6042d1e0#gistcomment-3461639

Thanks all to those improving this, pass it on 👍

const updateUrlParameter = (uri: string, key: string, value: string | null) => {
  // remove the hash part before operating on the uri
  const i = uri.indexOf('#');
  const hash = i === -1 ? '' : uri.substr(i);
  uri = i === -1 ? uri : uri.substr(0, i);

  const re = new RegExp(`([?&])${key}=.*?(&|$)`, 'i');
  const separator = uri.indexOf('?') !== -1 ? '&' : '?';

  if (value === null) {
    // remove key-value pair if value is specifically null
    uri = uri.replace(new RegExp(`([?&]?)${key}=[^&]*`, 'i'), '');
    if (uri.slice(-1) === '?') {
      uri = uri.slice(0, -1);
    }
    // replace first occurrence of & by ? if no ? is present
    if (uri.indexOf('?') === -1) uri = uri.replace(/&/, '?');
  } else if (uri.match(re)) {
    uri = uri.replace(re, `$1${key}=${value}$2`);
  } else {
    uri = `${uri + separator + key}=${value}`;
  }
  return uri + hash;
};

It worth to publish it on NPM. I was really surprised today that there is no package to manipulate non-absolute URLs 😅