get or set URL parameters with replaceState

get-post-parameters.js

/*
GETs and POSTs URL parameters

handleParam('get', ['key', 'foo'])
> { 'key' : 'value', 'foo' : 'bar'}

handleParam('post', {'key':'value', 'foo': bar})
*/

function handleParam(method, data){
  var baseUrl = [location.protocol, '//', location.host, location.pathname].join('');
  var urlQueryString = location.search;
  var hash = location.hash;

  /* GET PARAMETERS FROM URL */
  if(method === 'get') {

    if(typeof data == 'string') {
    //Single parameter to get

      var key = data;
      //Look for parameter in URL
      var pattern = new RegExp('('+key+')(=)([0-9\\w_\\-]+)', 'g');
      /*
      exec returns either null or something like
      ['key=value', 'key', '=', 'value'] <-- we want that last item
      */
      var search = pattern.exec(urlQueryString);
      return search !== null ? search[search.length-1] : undefined;

    } else if(typeof data == 'object') {
    //Array of parameters to get

      //Object to return
      var p = {};
      for(var i = 0, ct = data.length; i < ct; i++) {
        var key = data[i];
        var pattern = new RegExp('('+key+')(=)([0-9\\w_\\-]+)', 'g');
        //Look for parameter in URL
        var match = pattern.exec(urlQueryString);
        //If key exists, save the value, otherwise undefined
        p[key] = match !== null ? match[match.length-1] : undefined;
      }

      return p;

    }
  }
  /* SET PARAMETERS IN URL */
  else if(method === 'post') {

    // Perform text transforms on a copy (nqs --> newQueryString)
    var nqs = urlQueryString !== "" ? urlQueryString : '?';

    for(key in data) {
      // new value
      var value = data[key];
      // Finds something like: ['key=value', 'key', '=', 'value']
      var pattern = new RegExp('('+key+')(=)([0-9\\w_\\-]+)', 'g');
      var match = pattern.exec(nqs);

      var newParam;
      //If parameter already exists in URL
      if(match !== null) {
        var exParam = match[0];
        //Drop the full parameter & the existing value
        match = match.slice(1, match.length-1);
        //Add the new value
        match.push(value);
        //Construct string parameter
        newParam = match.join('');
        //Replace existing parameter with new parameter
        nqs = nqs.replace(exParam, newParam);
      }
      //If parameter doesn't exist in URL
      else {
        //Append key and value to URL
        if(nqs.length == 0) {
          nqs = '?';
        } else if(nqs.length > 1 && nqs.indexOf('?') == 0) {
          nqs = nqs + '&';
        }
        nqs = nqs + key + '=' + value;
      }
    }
    //Update URL state without refreshing
    window.history.replaceState({}, "", baseUrl + nqs + hash);
  }
}