querystring/encode.js

const stringifyPrimitive = v => {
  switch (typeof v) {
    case 'string':
      return v;

    case 'boolean':
      return v ? 'true' : 'false';

    case 'number':
      return isFinite(v) ? v : '';

    default:
      return '';
  }
};

export const encode = (obj, sep, eq, name) => {
  sep = sep || '&';
  eq = eq || '=';
  if (obj === null) {
    obj = undefined;
  }

  if (typeof obj === 'object') {
    return Object.keys(obj).map(k => {
      const ks = encodeURIComponent(stringifyPrimitive(k)) + eq;
      if (Array.isArray(obj[k])) {
        return obj[k].map(v => ks + encodeURIComponent(stringifyPrimitive(v))).join(sep);
      } else {
        return ks + encodeURIComponent(stringifyPrimitive(obj[k]));
      }
    }).filter(Boolean).join(sep);

  }

  if (!name) return '';
  return encodeURIComponent(stringifyPrimitive(name)) + eq +
         encodeURIComponent(stringifyPrimitive(obj));
};