jquery延迟返回太早

Question

我有以下代码：

$.when(multipleQueries(stateQueries, rowData))
    .then(function (data) {
        //do stuff with data - removed for brevity

multipleQueries 函数如下：

function multipleQueries(queriesToExecute, rowData) {
    var allQueriesMapped = $.Deferred();

    // If a single query has been provided, convert it into an array
    if (Array.isArray(queriesToExecute) === false) {
        queriesToExecute = [].concat(queriesToExecute);
    }

    // Create a function for each region to run the query.
    $.when.apply($, $.map(queriesToExecute, function (query) {

        // Execute the query in the region
        return $.when(executeQuery(query.InstanceInfo, query.Query)).then(function (data) {
            var isDataMapped = $.Deferred();
            var mappedData = [];
            // Perform some data transformation
            $.when.apply($, $.map(data.results, function (value) {
                var properties = value.succinctProperties;
                 //code removed for brevity
                return $.when(mapData(properties)).then(function (mappedRow) {
                    if (mappedRow) {
                        mappedData.push(mappedRow);
                    }
                });
            })).then(function () {
                isDataMapped.resolve({
                    results: mappedData,
                    numItems: mappedData.length
                });
            });
            return isDataMapped.promise();
        }).then(function (data) {
            debugger;
            allQueriesMapped.resolve(data);
        });
    }));

    return allQueriesMapped.promise();
}

我遇到的问题是，我传入了 5 个查询以执行到 multipleQueries 函数，但在运行第一个查询后它正在运行调试器行 - 然后解决 allQueriesMapped deferred，然后它返回到 do包含调用它的数据的东西，但是因为我没有来自我传入的 5 个 queires 的所有数据，所以我没有看到预期的行为 - 我如何设置这些承诺有什么遗漏吗？

注意 - 我尝试将调试器之前的 .then 更改为 .done 但得到相同的行为，并且还尝试将调用代码更改为 .done 如下所示但也得到相同的结果。

$.when(multipleQueries(stateQueries, rowData))
    .done(function (data) {
        //do stuff with data - removed for brevity

** 更新——执行查询函数如下

function executeQuery(instanceInfo, query) {
    return $.ajax({
        url: instanceInfo.Url,
        type: 'GET',
        data: {
            q: query,
            succinct: true
        },
        processData: true
    });
}

Answer 1

正如freedomn-m 和charlietfl 指出的那样，这个then 放错地方了（见*** 评论）：

function multipleQueries(queriesToExecute, rowData) {
    var allQueriesMapped = $.Deferred();

    // If a single query has been provided, convert it into an array
    if (Array.isArray(queriesToExecute) === false) {
        queriesToExecute = [].concat(queriesToExecute);
    }

    // Create a function for each region to run the query.
    $.when.apply($, $.map(queriesToExecute, function(query) {

        // Execute the query in the region
        return $.when(executeQuery(query.InstanceInfo, query.Query)).then(function(data) {
            var isDataMapped = $.Deferred();
            var mappedData = [];
            // Perform some data transformation
            $.when.apply($, $.map(data.results, function(value) {
                var properties = value.succinctProperties;
                //code removed for brevity
                return $.when(mapData(properties)).then(function(mappedRow) {
                    if (mappedRow) {
                        mappedData.push(mappedRow);
                    }
                });
            })).then(function() {
                isDataMapped.resolve({
                    results: mappedData,
                    numItems: mappedData.length
                });
            });
            return isDataMapped.promise();
        }).then(function(data) {                    // ***
            debugger;                               // ***
            allQueriesMapped.resolve(data);         // ***
        });
    }));

    return allQueriesMapped.promise();
}

它在map里面，什么时候它应该在它外面：

function multipleQueries(queriesToExecute, rowData) {
    var allQueriesMapped = $.Deferred();

    // If a single query has been provided, convert it into an array
    if (Array.isArray(queriesToExecute) === false) {
        queriesToExecute = [].concat(queriesToExecute);
    }

    // Create a function for each region to run the query.
    $.when.apply($, $.map(queriesToExecute, function(query) {

        // Execute the query in the region
        return $.when(executeQuery(query.InstanceInfo, query.Query)).then(function(data) {
            var isDataMapped = $.Deferred();
            var mappedData = [];
            // Perform some data transformation
            $.when.apply($, $.map(data.results, function(value) {
                var properties = value.succinctProperties;
                //code removed for brevity
                return $.when(mapData(properties)).then(function(mappedRow) {
                    if (mappedRow) {
                        mappedData.push(mappedRow);
                    }
                });
            })).then(function() {
                isDataMapped.resolve({
                    results: mappedData,
                    numItems: mappedData.length
                });
            });
            return isDataMapped.promise();
        });
    })).then(function(data) {
        debugger;
        allQueriesMapped.resolve(data);
    });

    return allQueriesMapped.promise();
}

但是其中有很多不必要地使用$.when 和new $.Deferred（请参阅*** 1 cmets），您可以更简单地将参数包装在一个数组中（请参阅@ 987654331@评论：

function multipleQueries(queriesToExecute, rowData) {
    // If a single query has been provided, convert it into an array
    if (Array.isArray(queriesToExecute) === false) {
        queriesToExecute = [queriesToExecute]; // *** 2
    }

    // Create a function for each region to run the query.
    return $.when.apply($, $.map(queriesToExecute, function(query) { // *** 1

        // Execute the query in the region
        return executeQuery(query.InstanceInfo, query.Query).then(function(data) { // *** 1
            var mappedData = [];
            // Perform some data transformation
            return $.when.apply($, $.map(data.results, function(value) {
                var properties = value.succinctProperties;
                //code removed for brevity
                return mapData(properties).then(function(mappedRow) { // *** 1
                    if (mappedRow) {
                        mappedData.push(mappedRow);
                    }
                });
            })).then(function() {
                return {
                    results: mappedData,
                    numItems: mappedData.length
                };
            });
        });
    }));
}

当你已经有了一个承诺时，就再也没有必要通过new 创建一个新的承诺了；只需使用then 返回的那个。另外，当你已经有一个承诺时，就没有任何必要使用$.when(thePromise)。

您也可能受益于早期切换到内置的 promise 语义而不是 jQuery 的 Deferred：

function multipleQueries(queriesToExecute, rowData) {
    // If a single query has been provided, convert it into an array
    if (Array.isArray(queriesToExecute) === false) {
        queriesToExecute = [queriesToExecute];
    }

    // Create a function for each region to run the query.
    return Promise.all(queriesToExecute.map(function(query) {
        // Execute the query in the region
        return executeQuery(query.InstanceInfo, query.Query).then(function(data) {
            return Promise.all(data.results.map(function(value) {
                var properties = value.succinctProperties;
                //code removed for brevity
                return mapData(properties);
            }).then(function(mappedData) {
                mappedData = mappedData.filter(Boolean); // Remove the falsy ones from `mapData`
                return {
                    results: mappedData,
                    numItems: mappedData.length
                };
            });
        });
    }));
}

Promise.all 对于处理承诺数组非常有用。但请确保您使用的是最新的 jQuery，早期版本的 Deferred 无法与真正的 Promise 正确互操作。我不知道（也无法立即找到）何时修复。