ajax

var xhr = new XMLHttpRequest();

xhr.onreadystatechange = function(){
  if(httpRequest.readyState===4){
   if(httpRequest.status===200){
     var data = JSON.parse(httpRequest.response);
   }
  }
}

httpRequest.open('GET','https://api.github.com/users/ruanyf',true);
httpRequest.setRequestHeader("Content-Type","application/json");
httpRequest.send(null);

/**
 * @description: 
 * @param { 
 * 		method:方法
 * 		data: 参数
 * 		type: 返回数据类型
 * 		success: 响应成功后的会调
 * 		error: 响应失败后的会调
 * } option
 * @return {*}
 */
function request(option) {
  if(Object.prototype.toString.call(option) !== '[object, Object]') return undefined;

  option.method = option.method ? option.method.toUpperCase() : 'GET';
  option.data = option.data || {};
  option.type = option.type || 'json';

  var formData = [];
  for(key in option.data) {  
    formData.push(''.concat(key, '=', option.data[key]))
  }
  option.data = formData.join('&')

  if(option.method === 'GET' && formData.lenght > 0) {
    option.url += location.search.length === 0 ? ''.concat('?', option.data) : ''.concat('&', option.data);
  }


  var xhr = new XMLHttpRequest();
  xhr.responseType = option.type;
  xhr.withCredentials = false;  //指示是否应使用Cookie或授权标头等凭据进行跨站点访问控制请求。
  // 处理请求回调
  xhr.onreadystatechange = function() {
    if(xhr.readyState === 4) {
      if(xhr.status === 200) {
        if(option.success && typeof option.success === 'function') {
          option.success(xhr.response)
        }
      } else {
        if(option.error && typeof option.error === 'function') {
          option.error(new Error(xhr.statusText))
        }
      }
    }
  }
  xhr.open(option.method, option.url, true); // true 代表是异步请求
  // 如果是 POST 请求，需要设置请求头
  if (option.method === 'POST') {
    xhr.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded')
  }
  // 发送请求
  xhr.send(option.method === 'POST' ? option.data : null);
}

fetch('https://xxx.com/api/user')
  .then(res => res.json())
  .then(result => { console.log(result) })
	.catch(err => { console.log(err) })

fetch('https://xxx.com/api/user',{
  method: 'POST',
  headers: {},
  data: {},
  
})