如何通过JQuery ajaxSend事件覆盖成功函数

我试图覆盖 ajaxsend 事件的成功函数，但它不起作用 这是代码：

    $(document).ajaxSend(function(event,xhr,options){
        console.log('ajaxSend');
        var tempSuccess = options.success;
        options.success = function(data, textStatus, jqXHR){
            console.log('start');
            tempSuccess(data, textStatus, jqXHR);
            console.log('end');
        }; xhr.success = options.success;});

在 AJAX 上，我确实在控制台中看到“ajax”，但成功后我看不到开始和结束调试消息。

我做错了什么？

你想要完成的事情无法完成ajaxSend。问题是ajaxSend显然可以使用原件的副本xhr and options对象，因此修改不会产生任何效果。您可以使用以下代码轻松测试：

$(document).ajaxSend(function(event, xhr, options){
    delete options.success;
    console.log(options.success);   // undefined
});
$.ajax({
    url: "test.html",
    success: function() { console.log("this will be printed nevertheless"); }
});

所以你不能使用ajaxSend覆盖成功回调。相反，您必须“破解”jQuery 的 AJAX 函数：

// closure to prevent global access to this stuff
(function(){
    // creates a new callback function that also executes the original callback
    var SuccessCallback = function(origCallback){
        return function(data, textStatus, jqXHR) {
            console.log("start");
            if (typeof origCallback === "function") {
                origCallback(data, textStatus, jqXHR);
            }
            console.log("end");
        };
    };

    // store the original AJAX function in a variable before overwriting it
    var jqAjax = $.ajax;
    $.ajax = function(settings){
        // override the callback function, then execute the original AJAX function
        settings.success = new SuccessCallback(settings.success);
        jqAjax(settings);
    };
})();

现在您可以简单地使用$.ajax照常：

$.ajax({
    url: "test.html",
    success: function() {
        console.log("will be printed between 'start' and 'end'");
    }
});

据我所知，任何 jQuery 的 AJAX 函数（例如$.get() or .load()) 内部使用$.ajax，所以这应该适用于通过 jQuery 完成的每个 AJAX 请求（不过我还没有测试过......）。

---

Something like that should also work with "pure" JavaScript by hacking the XMLHttpRequest.prototype. Note that the following won't work in IE, which uses ActiveXObject instead of XMLHttpRequest.

(function(){
    // overwrite the "send" method, but keep the original implementation in a variable
    var origSend = XMLHttpRequest.prototype.send;
    XMLHttpRequest.prototype.send = function(data){
        // check if onreadystatechange property is set (which is used for callbacks)
        if (typeof this.onreadystatechange === "function") {
            // overwrite callback function
            var origOnreadystatechange = this.onreadystatechange;
            this.onreadystatechange = function(){
                if (this.readyState === 4) {
                    console.log("start");
                }
                origOnreadystatechange();
                if (this.readyState === 4) {
                    console.log("end");
                }
            };
        }
        // execute the original "send" method
        origSend.call(this, data);
    };
})();

用法（就像通常的 XMLHttpRequest 一样）：

var xhr = new XMLHttpRequest();
xhr.open("POST", "test.html", true);
xhr.onreadystatechange = function(){
    if (xhr.readyState === 4) {
        console.log("will be printed between 'start' and 'end'");
    }
};
xhr.send();