jquery-deferred - jQuery - 延迟等待一组 ajax 请求以完成甚至失败

Question

在许多ajax请求都完成后，无论它们是成功还是出错，如何执行函数？

我一直在尝试使用 $.when.apply(this, array)传递一组延迟的 jqXHR 对象。然而就像文档说的

In the multiple-Deferreds case where one of the Deferreds is rejected, jQuery.when immediately >fires the failCallbacks for its master Deferred. Note that some of the Deferreds may still be >unresolved at that point.

如何利用 jQuery 延迟对象始终等待所有 ajax 调用完成？

也许我应该创建自己的延迟来包装所有其他延迟？如果是这样，我不太清楚如何设置。

Answer 1

本着 Promise 规范在 future 可能会如何发展的精神，PromiseInspection对象，这是一个 jQuery 附加函数，它会告诉您所有 promise 何时完成，无论是履行还是拒绝:

(function() {    
    // pass either multiple promises as separate arguments or an array of promises
    $.settle = function(p1) {
        var args;
        if (Array.isArray(p1)) {
              args = p1;
        } else {
            args = Array.prototype.slice.call(arguments);
        }

        return $.when.apply($, args.map(function(p) {
            // make sure p is a promise (it could be just a value)
            p = wrapInPromise(p);
            // Make sure that the returned promise here is always resolved with a PromiseInspection object, never rejected
            return p.then(function(val) {
                return new PromiseInspection(true, val);
            }, function(reason) {
                // Convert rejected promise into resolved promise by returning a resolved promised
                // One could just return the promiseInspection object directly if jQuery was
                // Promise spec compliant, but jQuery 1.x and 2.x are not so we have to take this extra step
                return wrapInPromise(new PromiseInspection(false, reason));
            });
        })).then(function() {
              // return an array of results which is just more convenient to work with
              // than the separate arguments that $.when() would normally return
            return Array.prototype.slice.call(arguments);
        });
    }

    // utility functions and objects
    function isPromise(p) {
        return p && (typeof p === "object" || typeof p === "function") && typeof p.then === "function";
    }

    function wrapInPromise(p) {
        if (!isPromise(p)) {
            p = $.Deferred().resolve(p);
        }
        return p;
    }

    function PromiseInspection(fulfilled, val) {
        return {
            isFulfilled: function() {
                return fulfilled;
            }, isRejected: function() {
                return !fulfilled;
            }, isPending: function() {
                // PromiseInspection objects created here are never pending
                return false;
            }, value: function() {
                if (!fulfilled) {
                    throw new Error("Can't call .value() on a promise that is not fulfilled");
                }
                return val;
            }, reason: function() {
                if (fulfilled) {
                    throw new Error("Can't call .reason() on a promise that is fulfilled");
                }
                return val;
            }
        };
    }
})();

然后，您可以像这样使用它:

$.settle(promiseArray).then(function(inspectionArray) {
    inspectionArray.forEach(function(pi) {
        if (pi.isFulfilled()) {
            // pi.value() is the value of the fulfilled promise
        } else {
            // pi.reason() is the reason for the rejection
        }
    });
});

请记住， $.settle()将始终满足(从不拒绝)并且满足的值是 PromiseInspection 的数组对象，您可以询问每个对象以查看它是被满足还是被拒绝，然后获取相应的值或原因。有关示例用法，请参见下面的演示:

工作演示: https://jsfiddle.net/jfriend00/y0gjs31r/