Handling URL Parameters with plain javascript and Lodash

URLParameters.js

function URLParameters(str) {
  this.queryString = typeof(str) === 'undefined' ? document.location.search : str;
  this.params = {};

  this.parse = function(string) {
    if (string && !_.isEmpty(string)) {
      var obj = {};
      var pairs = string.replace('?', '').split('&');

      pairs = _.map(pairs, function(pair, index) {
        return pair.split('=');
      });

      _.forEach(pairs, function(pair, index) {
        obj[pair[0]] = obj[pair[0]] || [];
        obj[pair[0]].push(pair[1]);
      });

      return obj;
    } else {
      return {};
    }
  }

  this.toString = function() {
    if (this.isEmpty()) {
      return '';
    } else {
      var str = _.map(this.params, function(values, key) {
        return _.map(values, function(value) {
          return key + '=' + value;
        }).join('&');
      }).join('&');

      return ('?' + str);
    }
  }

  this.get = function(key) {
    return this.params[key];
  }

  this.set = function(key, value) {
    return this.params[key] = [value];
  }

  this.append = function(key, value) {
    this.params[key] = this.params[key] || [];
    return this.params[key].push(value);
  }

  this.delete = function(key) {
    return delete this.params[key];
  }

  this.deleteAll = function() {
    return this.params = {}
  }

  this.isEmpty = function() {
    return _.isEmpty(this.params);
  }

  this.params = this.parse(this.queryString);
}