class Ajax {
    constructor() {
        this.ajax = new XMLHttpRequest();
    }

    /**
     * 
     * @param {*} params 
     * {
     *   url: '',
     *   data: {
     *     id: 1,
     *     page: 2
     *   },
     *   header: {
     *     'Content-Type': 'application/x-www-form-urlencoded;charset=UTF-8'
     *   }
     * }
     */
    get(params) {
        return new Promise((success, error) => {
            var str = ""
            for (const key in params.data) {
                str += `&${key}=${params.data[key]}`
            }

            str = str.replace("&", "?")
            this.ajax.open("GET", `${config.checkUrl()}${params.url}${str}`)
            //由基地址 短地址 加参数组成
            this.ajax.send()
            this.readystatechange(success, error)
        })
    }

    post() { }

    readystatechange(success, error) {
        this.ajax.onreadystatechange = () => {
            if (this.ajax.readyState == 4) {
                if (this.ajax.status == 200) {
                    var data = JSON.parse(this.ajax.responseText)
                    success(this.checkStatus(data))
                    //如果http状态码和ajax状态码都请求成功就调用判断接口方法 this.checkStatus
                    
                } else {
                    error(this.ajax)
                }
            }
        }
    }
//判断接口的状态
    checkStatus(data) {
        switch (data.status) {
            case 200:
                return data.result
                break;
        
            case 404:
                alert(data.msg);
                throw new Error(data.msg)
             break;
            default:
                break;
        }
    }
}