封装Ajax

function FAjax(FOption){
    var paramStr = "?";
    var keysArr = Object.keys(FOption.data);
    var valuesArr = Object.values(FOption.data);
    for(let i=0; i<keysArr.length; i++){
        paramStr += keysArr[i] + "=" + valuesArr[i];
        paramStr += "&";
    }
    paramStr = paramStr.slice(0, paramStr.length-1);
    FOption.url += paramStr;
    var xhr = new XMLHttpRequest();
    xhr.open(FOption.type, FOption.url, FOption.async);
    xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
    xhr.send();
    xhr.onreadystatechange = function (){
        if(xhr.readyState == 4){
            if(xhr.status == 200){
                FOption.success(xhr.responseText);
            }
        }
    };
}