javascript 异步的替代方法：false ajax

alternative to async: false ajax

提问by rpsep2

I loop through an array running an ajax request for each. I need the requests to happen in order, so i can pick up the last request and run a function on success.

我循环遍历一个数组，为每个数组运行一个 ajax 请求。我需要按顺序发生请求，所以我可以选择最后一个请求并在成功时运行一个函数。

at the moment im running (simplified):

目前我正在运行（简化）：

$.each(array, function(i, item){
    ajax_request(item.id, item.title, i);
})

function ajax_request(id, title, i){
    $.ajax({
        async: false,
        url: 'url here',
        success: function(){
            if(i == array.length-1){
                // run function here as its the last item in array
            }
        }
    })
}

however, using async:false makes the application unresponsive/ slow. but, without async:false sometimes one of the requests will hang a bit and actually return after the last sent ajax request returns.

但是，使用 async:false 会使应用程序无响应/缓慢。但是，如果没有 async:false 有时其中一个请求会挂起一点并在最后发送的 ajax 请求返回后实际返回。

how can i implement this without using async:false ?

我如何在不使用 async:false 的情况下实现这一点？

回答by jfriend00

You can use a local function for running the ajax call and in each successive success handler, you can kick off the next ajax call.

您可以使用本地函数来运行 ajax 调用，并且在每个连续的成功处理程序中，您可以启动下一个 ajax 调用。

function runAllAjax(array) {
    // initialize index counter
    var i = 0;

    function next() {
        var id = array[i].id;
        var title = array[i].title;
        $.ajax({
            async: true,
            url: 'url here',
            success: function(){
                ++i;
                if(i >= array.length) {
                    // run function here as its the last item in array
                } else {
                    // do the next ajax call
                    next();
                }

            }
        });
    }
    // start the first one
    next();
}

---

---

Updating this answer in 2016 with an option that uses promises. Here's how you run the requests in series:

在 2016 年使用使用承诺的选项更新此答案。以下是您如何按顺序运行请求：

array.reduce(function(p, item) {
    return p.then(function() {
        // you can access item.id and item.title here
        return $.ajax({url: 'url here', ...}).then(function(result) {
           // process individual ajax result here
        });
    });
}, Promise.resolve()).then(function() {
    // all requests are done here
});

Here's how you run them in parallel, returning all the results:

以下是并行运行它们并返回所有结果的方法：

var promises = [];
array.forEach(function(item) {
    // you can access item.id and item.title here
    promises.push($.ajax({url: 'url here', ...});
});
Promise.all(promises).then(function(results) {
    // all ajax calls done here, results is an array of responses
});

回答by Kevin

You can put your AJAX code in a separate function and whenever a request finishes it can call this method and pass its identity which will be incremented for the next request.

您可以将您的 AJAX 代码放在一个单独的函数中，每当请求完成时，它都可以调用此方法并传递其身份，该身份将为下一个请求递增。

回答by Arun P Johny

Try $.when()

试试 $.when()

var requests = $.map(array, function (i, item) {
    return ajax_request(item.id, item.title, i);
});
$.when.apply($, requests).done(function(){
    $.each(arguments, function(i, params){
        var data = params[0];
        //do your stuff
    })
})

function ajax_request(id, title, i) {
    return $.ajax({
        async: false,
        url: 'url here'
    })
}