在JavaScript中的for循环中调用异步函数

I have the following code:

我有以下代码：

for(var i = 0; i < list.length; i++){
    mc_cli.get(list[i], function(err, response) {
        do_something(i);
    });
}

mc_cli is a connection to a memcached database. As you can imagine, the callback function is asynchronous, thus it may be executed when the for loop already ended. Also, when calling in this way do_something(i) it always uses the last value of the for loop.

mc_cli是与memcached数据库的连接。可以想象，回调函数是异步的，因此可以在for循环结束时执行。此外，当以这种方式调用do_something（i）它总是使用for循环的最后一个值。

I tried with a closure in this way

我用这种方式尝试了一个闭包

do_something((function(x){return x})(i))

but apparently this is again using always the last value of the index of the for loop.

但显然这又是使用for循环索引的最后一个值。

I also tried declaring a function before the for loop like so:

我也尝试在for循环之前声明一个函数，如下所示：

var create_closure = function(i) {
    return function() {
        return i;
    }
}

and then calling

然后打电话

do_something(create_closure(i)())

but again without success, with the return value always being the last value of the for loop.

但是再次没有成功，返回值始终是for循环的最后一个值。

Can anybody tell me what am I doing wrong with closures? I thought I understood them but I can't figure why this is not working.

任何人都可以告诉我我的闭包装有什么问题吗？我以为我理解了他们，但我无法理解为什么这不起作用。

8 个解决方案

#1

Since you're running through an array, you can simply use forEach which provides the list item, and the index in the callback. Iteration will have its own scope.

由于您正在运行数组，因此您可以简单地使用提供列表项的forEach和回调中的索引。迭代将有自己的范围。

list.forEach(function(listItem, index){
  mc_cli.get(listItem, function(err, response) {
    do_something(index);
  });
});

8 个解决方案

#1

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