class Http {
    defaultOption = {
        timeout: 6000,
        headers: {
            'Content-Type': 'application/json;charset=utf-8'
        }
    }

    constructor() {
        this.xhr = new XMLHttpRequest()
    }

    get(par) {
        return new Promise((success, error) => {
            this.setOption(par)
            let urlParams = ""
            for (const key in par.data) {
                urlParams += `&${key}=${par.data[key]}`
            }
            urlParams = urlParams.replace("&", "")
            this.xhr.open("GET", `${par.url}?${urlParams}`)
            this.xhr.timeout = this.defaultOption.timeout
            this.setHeader(par.headers)
            this.xhr.send()
            this.statechange(success, error);
        })
    }

    post(par) {
        return new Promise((success, error) => {
            this.setOption(par)
            this.xhr.open("POST", par.url)
            this.xhr.timeout = this.defaultOption.timeout
            this.setHeader(par.headers)
            this.xhr.send(JSON.stringify(par.data))
            this.statechange(success, error);
        })
    }

    setOption(par) {
        this.defaultOption.timeout = par.timeout || this.defaultOption.timeout
        // ....
    }

    setHeader(headerObject = {}) {
        Object.assign(headerObject, this.defaultOption.headers)
        for (const key in headerObject) {
            this.xhr.setRequestHeader(key, headerObject[key]);
        }
    }

    statechange(success, error) {
        this.xhr.onreadystatechange = () => {
            if (this.xhr.readyState == 4) {
                if (this.xhr.status == 200) {
                    let data = JSON.parse(this.xhr.response)
                    success(data)
                } else {
                    error(this.xhr)
                }
            }
        }
    }
}

var http = new Http();