如何将变量传递给匿名函数 [英] How to pass variable to anonymous function

问题描述

我想传递变量 setTimeout 函数并对其执行某些操作。当我提醒 i 的值时，它会显示我没想到的数字。我做错了什么？我想要从1到8的日志值。

I want to pass variable setTimeoutfunction and do something with that. When I alert value of i it shows me numbers that i did not expected. What i m doing wrong? I want log values from 1 till 8.

var end=8;
for (var i = 1; i < end; i ++) {
       setTimeout(function (i) {
           console.log(i);   

       }, 800);
   }

推荐答案

解决此问题的标准方法是使用工厂函数：

The standard way to solve this is to use a factory function:

var end=8;
for (var i = 1; i < end; i ++) {
       setTimeout(makeResponder(i), 800);
   }

function makeResponder(index) {
    return function () {
        console.log(index);   
   };
}

实例 | 来源

在那里，我们致电 makeResponder 在循环中，它返回一个函数，该函数关闭传递给它的参数（ index ）而不是 i 变量。 （这很重要。如果您刚从匿名函数中删除 i 参数，您的代码将部分工作，但所有函数都会看到<$ c $的值c>我当他们跑时，而不是他们最初安排时;在你的例子中，他们都看到 8 。）

There, we call makeResponder in the loop, and it returns a function that closes over the argument passed into it (index) rather than the i variable. (Which is important. If you just removed the i argument from your anonymous function, your code would partially work, but all of the functions would see the value of i as of when they ran, not when they were initially scheduled; in your example, they'd all see 8.)

更新来自您的评论：

...如果我以这种方式调用它将是正确的 setTimeout（makeResponder（i），i * 800）; ？

是的，如果您的目标是让每次通话比最后一次大约晚800毫秒发生，那么工作：

Yes, if your goal is to have each call occur roughly 800ms later than the last one, that will work:

实例 来源

我试过 setTimeout（makeResponder（i），setInterval（i））; function setInterval（index）{console.log（index * 800）;返回索引* 800; } 但它无法正常工作

您不使用 setInterval 这样，可能根本不想用它。

You don't use setInterval that way, and probably don't want to use it for this at all.

进一步更新：您在下面说过：

我需要先迭代打印8延迟8秒，第二次迭代打印7延迟7秒........打印2延迟2秒...打印0延迟0秒

I need first iteration print 8 delay 8 sec, second iteration print 7 delay 7 sec ........print 2 delay 2 sec ...print 0 delay 0 sec.

你刚才使用第二次超时再次应用上述原则：

You just apply the principles above again, using a second timeout:

var end=8;
for (var i = 1; i < end; i ++) {
       setTimeout(makeResponder(i), i * 800);
   }

function makeResponder(index) {
    return function () {
        var thisStart = new Date();
        console.log("index = " + index + ", first function triggered");
        setTimeout(function() {
            console.log("index = " +
                        index +
                        ", second function triggered after a further " +
                        (new Date() - thisStart) +
                        "ms delay");
        }, index * 1000);
   };
}

实例 | 来源

我想你现在有了你需要的所有工具。

I think you now have all the tools you need to take this forward.

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