javaScript

function getData(){
	if(window.XMLHttpRequest{
	var xhr = new XMLHttpRequest()
	}else{
	var xhr = new ActiveXObject("Microsoft.XMLHttp")
	}
}
// 打开ajax, 布尔值（fasle是同步，true是异步，因为ajax本身就是异步）
xhr.open("get","/student.do",true)
xhr.send()
xhr.onreadystatechange = function(){
	// 0=未初始化,1=读取中，2=已读取，3=交互中，4=完成
  if(xhr.readyState == 4 && xhr.status == 200){
  	var data = JSON.pasre(xhr.responseText)
  	
  }
}
// 删除数据
function delData(){
xhr.open("get","/delStu.do?stuId="+stuId,true)
xhr.send()
  //post请求头
xhr.setRequestHeader("content-type","application/x-www-form-urlencoded")
xhr.onreadystatechange = function(){
	if(window.XMLHttpRequest{
		var xhr = new XMLHttpRequest()
	}else{
		var xhr = new ActiveXObject("Microsoft.XMLHttp")
	}
  if(xhr.readyState == 4 && xhr.status == 200){
  	var data = JSON.pasre(xhr.responseText)
			//服务器sql语句 delete from t_student where s_id = ?
  }
}
}

fetch(url).then(response => response.json())
  .then(data => console.log(data))
  .catch(e => console.log("Oops, error", e))
fetch('https://...', {
    method: 'post',
    body: JSON.stringify(base),
    headers: {
      'Content-Type': 'application/json'
    }
  }).then(function(data) {
 
})
## fetch封装
export default async(url='',data={},type='GET',method='fetch') => {
    type = type.toUpperCase();
    url = baseUrl + url;

    if (type == 'GET') {
        let dataStr = ''; //数据拼接字符串
        Object.keys(data).forEach(key => {
            dataStr += key + '=' + data[key] + '&';
        })

        if (dataStr !== '') {
            dataStr = dataStr.substr(0, dataStr.lastIndexOf('&'));
            url = url + '?' + dataStr;
        }
    }

    if (window.fetch && method == 'fetch') {
        let requestConfig = {
            credentials: 'include',//为了在当前域名内自动发送 cookie ， 必须提供这个选项
            method: type,
            headers: {
                'Accept': 'application/json',
                'Content-Type': 'application/json'
            },
            mode: "cors",//请求的模式
            cache: "force-cache"
        }

        if (type == 'POST') {
            Object.defineProperty(requestConfig, 'body', {
                value: JSON.stringify(data)
            })
        }
        
        try {
            const response = await fetch(url, requestConfig);
            const responseJson = await response.json();
            return responseJson
        } catch (error) {
            throw new Error(error)
        }
    } else {
        return new Promise((resolve, reject) => {
            let requestObj;
            if (window.XMLHttpRequest) {
                requestObj = new XMLHttpRequest();
            } else {
                requestObj = new ActiveXObject;
            }

            let sendData = '';
            if (type == 'POST') {
                sendData = JSON.stringify(data);
            }

            requestObj.open(type, url, true);
            requestObj.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
            requestObj.send(sendData);

            requestObj.onreadystatechange = () => {
                if (requestObj.readyState == 4) {
                    if (requestObj.status == 200) {
                        let obj = requestObj.response
                        if (typeof obj !== 'object') {
                            obj = JSON.parse(obj);
                        }
                        resolve(obj)
                    } else {
                        reject(requestObj)
                    }
                }
            }
        })
    }
}

##数组转伪数组	
[].push.apply(obj,arr);
##伪数组转数组
[].slice.call(arr,obj);