jquery上的多个ajax请求$ .when

Question

在 jquery 上使用 $.when 进行延迟 ajax 有一些缺点。成功处理 ajax 调用真是太好了。但是，如果一个失败，您将无法获得另一个请求的其他数据。

例如

var ajax1Success = function() { 返回 $.ajax(...); }; var ajax2Success = function() { 返回 $.ajax(...); }; var ajax3BoundtoFail = function() { 返回 $.ajax(...); }; $.when(ajax1Succes(), ajax2Success(), ajax3BoundtoFail()).done(function(a1, a2, a3) { // 都好 }).失败（函数（）{ // 不好... ajax3 注定会失败 });

任何好的解决方案如何从成功的ajax请求中获取其他数据？

Answer 1

$.when() 具有“快速失败”设计。这意味着第一个失败的承诺会导致$.when() 拒绝，而您只会得到拒绝信息。来自 jQuery 文档：

只要所有的 Deferred 解决，或拒绝 master Deferred，只要其中一个 延期被拒绝

但是，您可以使用不同类型的函数来监控您的一组承诺。这种类型的功能通常称为“结算”，您可以在其中等待所有承诺结算，然后从所有承诺中获取结果，无论它们是解决还是拒绝。

这是我过去使用的 jQuery promies 的一个实现，您可以像这样使用：

$.settle([ajax1Succes(), ajax2Success(), ajax3BoundtoFail()]).then(function(results) {
    // results is an array of PromiseInspection Objects
    // for each of them, you can see if the corresponding promise
    // succeeded with a value or failed with an error
    results.forEach(function(pi, index) {
        if (pi.isFulfilled()) {
            console.log("Promise #" + (index + 1) + " succeeded with result " + pi.value());
        } else {
            console.log("Promise #" + (index + 1) + " failed with reason " + pi.reason());
        }
    });
});

或者，如果您不需要确切的错误，可以使用更简单的版本：

$.settleVal(null, [ajax1Succes(), ajax2Success(), ajax3BoundtoFail()]).then(function(results) {
    // results contains the results from all the successful promises
    // any promises that has an error will show null as the result
});

请注意，它们使用的接口更像标准 Promise.all()，它们接受一组承诺并解析一组结果，因为这通常更容易在现实世界中使用。

还有，这是实现：

(function() {    

    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;
            }
        };
    }

    // 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);
            // Now we know for sure that p is a promise
            // 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);
        });
    }

    // simpler version that just converts any failed promises
    // to a resolved value of what is passed in, so the caller can just skip
    // any of those values in the returned values array
    // Typically, the caller would pass in null or 0 or an empty object
    $.settleVal = function(errorVal, p1) {
        var args;
        if (Array.isArray(p1)) {
              args = p1;
        } else {
            args = Array.prototype.slice.call(arguments, 1);
        }
        return $.when.apply($, args.map(function(p) {
            p = wrapInPromise(p);
            return p.then(null, function(err) {
                return wrapInPromise(errorVal);
            });
        }));
    }
})();