Build a query param string

build-query-param-string.js

/* 
  This function is meant to deal with lots of nonsense.
  Ideally it would enjoy something like the following:
  
    buildQueryParamString(['cool', 'okay'], '');
    > "?cool&okay"
    buildQueryParamString([['nifty', 'false'], ['neat', 'true']], '');
    > "?nifty=false&neat=true"
    buildQueryParamString([['wow', 'goodJob']], '?alreadyGotStarted=sureDid');
    > "?alreadyGotStarted=sureDid&wow=goodJob"

  If you give something like this it'll be alright. Or it'll do its best:

    buildQueryParamString([['why', 'though', 100000, { okay: 'great' }]], 'bler???rrrr');
    > "?why=though"
   
  This'll make it pretty sad though:

    buildQueryParamString(['que?ti&n', [{ hehe: 'evil' }, [undefined]]], '');
    > "?que?ti&n&[object Object]="

  So don't do that please.
*/
const buildQueryParamString = (paramsToAdd = [], builtString = '') => {
  const builtStringLength = builtString.length;
  const builtStringIsValid = builtStringLength && builtString[0] === '?';

  // the first argument isn't an array or is empty
  if (!Array.isArray(paramsToAdd) || !paramsToAdd?.length) {
    // return second argument, if valid, or '?'
    return builtStringIsValid ? builtString : '?';
  }

  let builtStringAndDelimiter;

  // discard second argument if invalid
  if (!builtStringIsValid) {
    builtStringAndDelimiter = '?';
  } else {
    // decide whether to add '&'
    const lastCharacter = builtString[builtStringLength - 1];
    const needsDelimiter = lastCharacter !== '?' && lastCharacter !== '&';
    const delimiter = needsDelimiter ? '&' : '';

    builtStringAndDelimiter = `${builtString}${delimiter}`;
  }

  // is the next one 'oneOfThese' or ['one', 'ofThese']?
  const nextParamRaw = paramsToAdd[0];
  const nextParamIsKeyValuePair = Array.isArray(nextParamRaw) && nextParamRaw.length > 1;
  // 'oneOfThese' or 'one=ofThese'
  const nextParam = nextParamIsKeyValuePair ? `${nextParamRaw[0]}=${nextParamRaw[1]}` : nextParamRaw;

  // '?oldStuff&oneOfThese' or '?oldStuff&one=ofThese'
  const newBuiltString = `${builtStringAndDelimiter}${nextParam}`;

  // we're done
  if (paramsToAdd.length === 1) {
    return newBuiltString;
  }

  // we're not -- recurse! 🌀
  return buildQueryParamString(paramsToAdd.slice(1), newBuiltString);
};