我使用jQuery。而且我不想在我的应用程序上进行并行AJAX调用,每个调用都必须等待上一个调用之后才能开始。如何执行呢?有帮手吗?
更新 如果我想知道XMLHttpRequest或jQuery.post的任何同步版本。但是顺序!=同步,我想要一个异步和顺序解决方案。
有比使用同步ajax调用更好的方法。jQuery ajax返回一个延迟,因此您可以使用管道链接来确保每个ajax调用在下一次运行之前完成。这是一个工作示例,其中包含更深入的示例,您可以在jsfiddle上使用它。
// How to force async functions to execute sequentially // by using deferred pipe chaining. // The master deferred. var dfd = $.Deferred(), // Master deferred dfdNext = dfd; // Next deferred in the chain x = 0, // Loop index values = [], // Simulates $.ajax, but with predictable behaviour. // You only need to understand that higher 'value' param // will finish earlier. simulateAjax = function (value) { var dfdAjax = $.Deferred(); setTimeout( function () { dfdAjax.resolve(value); }, 1000 - (value * 100) ); return dfdAjax.promise(); }, // This would be a user function that makes an ajax request. // In normal code you'd be using $.ajax instead of simulateAjax. requestAjax = function (value) { return simulateAjax(value); }; // Start the pipe chain. You should be able to do // this anywhere in the program, even // at the end,and it should still give the same results. dfd.resolve(); // Deferred pipe chaining. // What you want to note here is that an new // ajax call will not start until the previous // ajax call is completely finished. for (x = 1; x <= 4; x++) { values.push(x); dfdNext = dfdNext.pipe(function () { var value = values.shift(); return requestAjax(value). done(function(response) { // Process the response here. }); }); }
有些人说他们不知道代码做什么。为了理解它,您首先需要了解javascript promises。我敢肯定,诺言很快就会成为本地javascript语言功能,因此这应该给您学习的良好动力。