Javascript关闭不工作 [英] Javascript closure not working

问题描述

我已阅读以下问题：

• JavaScript闭环内循环 - 简单实用示例




• 如何传递JS的值（而不是引用）变量到函数？

• JavaScript closure inside loops – simple practical example
• How do JavaScript closures work?
• How do I pass the value (not the reference) of a JS variable to a function?

并尝试应用他们的解决方案（以及至少1/2 a

and tried to apply their solutions (as well as at least 1/2 a dozen other implementations) and none of them are working.

下面是具有循环的函数：

Here's the function that has the loop:

ExecuteQueryWhereQueryAndParamsBothArrays: function (queryArray, paramsArray, idsArray, success, fail, errorLogging) {
            var hasError = false;
            $rootScope.syncDownloadCount = 0;
            $rootScope.duplicateRecordCount = 0;

            $rootScope.db.transaction(function (tx) {
                for (var i = 0; i < paramsArray.length; i++) {
                    window.logger.logIt("id: " + idsArray[i]);

                    var query = queryArray[i];
                    var params = paramsArray[i];
                    var id = idsArray[i];

                    tx.executeSql(query, params, function (tx, results) {
                        incrementSyncDownloadCount(results.rowsAffected);
                    }, function(tx, error) {
                        if (error.message.indexOf("are not unique") > 0 || error.message.indexOf("is not unique") > 0) {
                            incrementDuplicateRecordCount(1);
                            return false;
                        }

// this didn't work:    errorLogging(tx, error, id);
// so I wrapped in in an IIFE as suggested:
                        (function(a, b, c) {
                            errorLogging(a, b, idsArray[c]);
                        })(tx, error, i);

                        return true;
                    });
                }
            }, function () {
                fail();
            }, function () {
                success();
            });

这里是errorLogging函数，正在写我的消息（注意，我不能 消息在同一个javascript文件中，因为我需要[angular]注入另一个引用到这个文件，它会导致循环引用，代码将不会运行）

And here's the errorLogging function that is writing my message (Note, I'm not able to "write" the message in the same javascript file because I'd need to [angular] inject another reference into this file and it would cause a circular reference and the code won't run)

var onError = function (tx, e, syncQueueId) {
    mlog.LogSync("DBService/SQLite Error: " + e.message, "ERROR", syncQueueId);
};

我可以实现什么其他方法来阻止它返回同步记录的最后一个id （当只有第一个记录有错误）？

What other method can I implement to stop it from returning the very last "id" of my sync records (when it's only the first record that has the error)?

推荐答案

… var i …
async(function() { …
//  errorLogging(tx, error, id);
    (function(a, b, c) {
        errorLogging(a, b, idsArray[c]);
    })(tx, error, i);
… })

这是没用的，因为 i 变量已经有错误的值。你需要将封装器放在整个异步回调函数中，关闭所有的变量都会在异步回调函数中使用，但会被同步回路修改。

That's rather useless, because the i variable already does have the wrong values there. You need to put the wrapper around the whole async callback, closing over all variables are used within the async callback but are going to be modified by the synchronous loop.

方式（总是工作）是简单地包装整个循环体，并关闭迭代变量：

The easiest way (works always) is to simply wrap the complete loop body, and close over the iteration variable:

for (var i = 0; i < paramsArray.length; i++) (function(i) { // here
    var query = queryArray[i];
    var params = paramsArray[i];
    var id = idsArray[i];

    window.logger.logIt("id: " + id);
    tx.executeSql(query, params, function (tx, results) {
        incrementSyncDownloadCount(results.rowsAffected);
    }, function(tx, error) {
        if (error.message.indexOf("are not unique") > 0 || error.message.indexOf("is not unique") > 0) {
            incrementDuplicateRecordCount(1);
            return false;
        }
        errorLogging(tx, error, id);
        return true;
    });
}(i)); // and here

你也可以传递循环中构造的所有变量迭代变量）作为闭包参数。在你的case，它可能看起来像这样：

You also might pass all variables that are constructed in the loop (and depend on the iteration variable) as the closure arguments. In your case, it might look like this:

for (var i = 0; i < paramsArray.length; i++) {
    (function(query, params, id) { // here
        window.logger.logIt("id: " + id);
        tx.executeSql(query, params, function (tx, results) {
            incrementSyncDownloadCount(results.rowsAffected);
        }, function(tx, error) {
            if (error.message.indexOf("are not unique") > 0 || error.message.indexOf("is not unique") > 0) {
                incrementDuplicateRecordCount(1);
                return false;
            }
            errorLogging(tx, error, id);
            return true;
        });
    }(queryArray[i], paramsArray[i], idsArray[i])); // here
}

或者你确定async回调函数， / p>

Or you identify the async callback, and wrap only that:

for (var i = 0; i < paramsArray.length; i++) {
    window.logger.logIt("id: " + idsArray[i]);
    tx.executeSql(queryArray[i], paramsArray[i], function (tx, results) {
        incrementSyncDownloadCount(results.rowsAffected);
    }, (function(id) { // here
        return function(tx, error) {
//      ^^^^^^ and here
            if (error.message.indexOf("are not unique") > 0 || error.message.indexOf("is not unique") > 0) {
                incrementDuplicateRecordCount(1);
                return false;
            }
            errorLogging(tx, error, id);
            return true;
        };
    }(idsArray[i]))); // and here
}

这篇关于Javascript关闭不工作的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！