QueryString manipulator

Fun functional object version

// Fun to write an understand version
var R = require('ramda');

function queryToObject(qString) {
  // strip ?
  // split on &
  // split on =
  // fromPairs
  var noQuestionMark = qString.slice(1); 
  var kvArray = noQuestionMark.split('&');
  var pairs = R.map(function(string) { return string.split('=') }, kvArray);
  return R.fromPairs(pairs);

  // return R.fromPairs(
  //          R.map(function(string) { return string.split('='),
  //                qString.slice(1).split('&')}));
}

function objectToQuery(obj) {
  var pairs = R.toPairs(obj);
  var kvArray = R.map(function(kvArr) { return kvArray.join('=') }, pairs);
  return '?' + kvArray.join('&');
}

function unpackThenRepack(fn, obj) {
  return objectToQuery(fn(queryToObject(obj)));
}

function addToQuery(qString, key, value) {
  var obj = queryToObject(qString);
  obj[key] = value;
  return objectToQuery(obj);
  // Abuse lexical scoping
  // return unpackThenRepack(function(obj) {
  //   obj[key] = value;
  //   return obj;
  // });
}

function removeFromQuery(qString, key) {
  var obj = queryToObject(qString);
  delete obj[key];
  return objectToQuery(obj);
  // return unpackThenRepack(function(obj) {
  //   delete obj[key]
  //   return obj;
  // });
}

function largestKey(qString) {
  var obj = queryToObject(qString);
  var keys = R.keys(obj); // Could also use Object.keys as well
  var sortedKeys = R.sort(function(a, b) {
    return b.length - a.length; // largest first... I think.
  }, keys);

  return R.head(sortedKeys); // head is the same as first

  // return R.head(
  //          R.sort(function(a, b) { return b.length - a.length },
  //                 R.keys(queryToObject(qString))));
}

// shorter names bc they're bound to the module
// The larger names show up in stack traces
module.exports = {
  q2Obj: queryToObject,
  obj2Q: objectToQuery,
  add: addToQuery,
  remove: removeFromQuery,
  largestKey: largestKey
};

Manipulator usage

var qStringer = require('qString');

var qString = '?key1=val1&key2=val2&key3=val3';

var qString2 = qStringer.add(qString, 'largest', 'this');
// ~ '?key1=val1&key2=val2&key3=val3&largest=this';

var qString3 = qStringer.remove(qString2, 'key2');
// ~ '?key1=val1&key3=val3&largest=this';

var largest = qStringer.largestKey(qString2);
// 'largest'

Pragmatic Version

// Pragmatic getter done version
function addToQuery(qString, key, value) {
  return qString + key + '&' + value;
}

function removeFromQuery(qString, key) {
  var kvArray = qString.slice(1).split('&');
  var filteredArray = kvArray.filter(function(string) {
    return !(string.indexOf(key + '=') + 1); // JavaScript -1 is truthy D':
  });
  return '?' + filteredArray.join('&');
}

function largestKey(qString) {
  // loop through once, collecting a temp largest key
  // A key is the space between & and =
  // return the largest key found
  var largest = '';
  var temp = '';
  var char = '';
  var addingToggle = true;

  // i starts at 1 bc qString[0] === ? always
  for(var i = 1; i < qString.length; i++) {
    char = qString[i];
    if (char === '=') {
      if (temp.length > largest.length) {
        largest = temp;
      }
      addingToggle = false;
    } else if (char === '&') {
      addingToggle = true;
    } else if (addingToggle) {
      temp += char;
    }
    // Otherwise, skip all values
  }

  return largest;
}

module.exports = {
  add: addToQuery,
  remove: removeFromQuery,
  largestKey: largestKey
};