class ajax {
    constructor() {  // 类的参数初始化
        this.baseUrl = config.checkBaseUrl();
        this.xhr = new XMLHttpRequest();
    }


    /**
     * 
     * @param {*} params 
     * {
     *   url: 'http://127.0.0.1:3000/api/index/threeMeals',
     *   data: {
     *     page: 1,
     *     id: 1
     *   },
     *   success: function() {}
     * }
     */
    get(params) {
        return new Promise((resolve, reject) => {
            if (params.hasOwnProperty("data")) {
                var str = ""
                for (const key in params.data) {
                    str += `&${key}=${params.data[key]}`
                }
                str = str.replace("&", "?")

                // 设置请求地址
                this.xhr.open("GET", `${this.baseUrl}${params.url}${str}`)
                //
                this.xhr.send();

                // 状态监听
                return this.onreadystatechange(resolve,reject)


            } else {
                throw new Error("data参数必传")
            }
        })
    }



    onreadystatechange(resolve,reject) {
        this.xhr.onreadystatechange = () => {

            if (this.xhr.readyState == 4) {
                if (this.xhr.status == 200) {
                    var res = JSON.parse(this.xhr.response);
                    switch (res.status) {
                        case 200:
                            resolve(res.result)
                            break;
                        case 404:
                            alert(res.msg);
                            throw new Error(res.msg);
                            break;
                    }
                } else {
                    alert("网络请求错误")
                }
            }
        }
    }
}

var http = new ajax();