Why my Json stringify slower then JSON.stringify

Question

So I am trying to understand why my code that stringify an object is much slower then JSON.stringify.

I cant think of a reason for this.

could someone share why this is hapning.

here is my test code that I wrote.

let data = {
  name: "test",
  id: 3,
  hidden: false,
  children: []
};
for (let i = 0; i < 7000; i++)
  data.children.push({ text: "gh", value: "gg" });
let name = null;
let start = t => {
  name = t;
  console.time(t);
};

let end = () => {
  console.timeEnd(name);
};
const ptype = {
  number: true,
  boolean: true
};

const stype = {
  string: true,
  function: true,
  date: true
};
const alltypes = { ...ptype, ...stype };
let stringify = json => {
  if (json === null || json === undefined)
    return undefined;
  let str = "";
  let type = typeof json;
  if (type === "object" && Array.isArray(json)) {
    str += "[";
    let c = "";
    for (let item of json) {
      str += c + stringify(item);
      if (c === "") c = ",";
    }
    str += "]";
    return str;
  }
  if (alltypes[type]) {
    if (ptype[type]) return json;
    return `\"${json}\"`;
  } else {
    str += "{";
    let c = "";
    for (let key in json) {
      str += `${c}\"${key}\":${stringify(
        json[key]
      )}`;
      if (c === "") c = ",";
    }
    str += "}";
  }
  return str;
};

start("JSON.parse");
let jsond = JSON.stringify(data);
end();
start("my stringify");
let myd = stringify(data);
end();