/**
 * @param {string} url
 * @param {string} method
 * @param {object} params
 * @returns
 */
function request(url, method = "GET", params = null) {
  return new Promise((resolve, reject) => {
    const xhr = new XMLHttpRequest()
    xhr.open(method, url)
    xhr.addEventListener("readystatechange", () => {
      if (xhr.readyState === 4) {
        if (xhr.status === 200) {
          resolve(xhr.responseText)
        } else {
          reject({
            code: xhr.status,
            response: xhr.response
          })
        }
      }
    })
    setTimeout(() => reject("timeout:1000"), 1000)
    xhr.send(JSON.stringify(params))
  })
}

request("http://localhost:3005/user/?name=saber&age=21").then(console.log)
request("http://localhost:3005/user/", "POST", {
  name: "saber",
  age: 233
}).then(console.log)

request("http://localhost:30051/user/?name=saber&age=21").then(console.log)
request("http://localhost:30051/user/", "POST", {
  name: "saber",
  age: 233
}).then(console.log)

Onreadystatechange

This function is called whenever the readyState property changes

ReadyState

0. The request is not initialized
1. Server connection established two。 Request received
2. Request processing
3. The request has been completed and the response is ready

Status http status code

1xx: request is being processed 2xx: request processing completed 3xx: redirect 4xx: Browser (client) error 5xx: server internal error