code: function stringify(obj) {
      var list = [];
      if ("object" === typeof obj && obj !== null) Object.keys(obj).map(it);
      return list.join("&");
  
      function it(key) {
        var val = obj[key];
        if ("undefined" === typeof val) return;
        if (val === null) return;
        // if (val === "") return;
        if (val instanceof Function) return;
        var pair = encodeURIComponent(key) + "=" + encodeURIComponent(val);
        list.push(pair);
      }
    }
docs: Stringify object as application/x-www-form-urlencoded representation.
  
  @class qs
  @function stringify
  @param obj {Object} plain key-value pair object
  @returns {string} application/x-www-form-urlencoded representation.
  @example
  var qs = require("qs-lite");
  
  var string = qs.stringify({foo: "bar", hoge: "pomu"}); // => "foo=bar&hoge=pomu"