什么是“这个"?参考下面的javascript? [英] What does "this" refer to in the following javascript?

问题描述

免责声明:我要问的是this的特定用途，而不是this的一般用途.因此，请没有google/copy/paste速度答案(:

DISCLAIMER: I am asking about a specific use of this, not what this is used for in general. So, please no google/copy/paste speed answers (:

我下面有javascript/jquery代码:

I have the javascript/jquery code below:

var req = {};

function getData()
{
    var fromPage = 0;
    var toPage = 1;

    req = $.ajax({
                    url: "/_vti_bin/lists.asmx",
                    type: "POST",
                    dataType: "xml",
                    data: xmlData,
                    complete: onSuccess,
                    error: function (xhr, ajaxOptions, thrownError) {
                        alert("error: " + xhr.statusText);
                        alert(thrownError);
                    },
                    contentType: "text/xml; charset=\"utf-8\""
                });

     req.fromPage = fromPage;
     req.toPage = toPage;
}

function onSuccess(resp) {
    alert(this.fromPage);
}

我发现代码在两个地方使用fromPage令人感到困惑(对不起，不是我的代码).

I find it pretty confusing that the code is using fromPage in two places (sorry not my code).

this是引用在getData内部声明的var还是作为req对象一部分的var?或也许完全是其他东西....

Does this refer to the var declared inside of getData or the one that is part of the req object? Or maybe something else entirely....

任何帮助表示赞赏.

推荐答案

根据 jQuery.ajax 文档:

According to jQuery.ajax documentation:

所有回调中的此引用是上下文选项中传递给设置中$ .ajax的对象；如果未指定上下文，则是对Ajax设置本身的引用.

The this reference within all callbacks is the object in the context option passed to $.ajax in the settings; if context is not specified, this is a reference to the Ajax settings themselves.

换句话说，由于您没有设置context选项，因此this将是作为参数传递给$.ajax的选项对象{...}.

In other words, since you didn't set the context option, this will be the options object {...} passed as the parameter to $.ajax.

您发布的代码似乎是错误的:它从错误的对象读取fromPage.如果在options对象上设置fromPage，它将起作用:

The code you posted seems wrong: it reads fromPage from the wrong object. It would work if you set fromPage on the options object instead:

req = $.ajax({
    //other options here...
    fromPage: fromPage
});

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