JavaScript：是否可以将变量传递给分配给变量的回调函数？
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JavaScript: Is it possible to pass a variable into a callback function that is assigned to a variable?
提问by Tarik
A lot of people say that this is asked too much in the comments, which made me hesitant to ask this, but I still have not found a solution in their answers, mostly because (1) they are typically using jQuery and (2) the questions usually contain technicalities I do not understand.
很多人说评论中问的太多了，这让我犹豫要不要问这个，但我仍然没有在他们的答案中找到解决方案，主要是因为（1）他们通常使用 jQuery 和（2）问题通常包含我不明白的技术细节。
I have a function with a variable inside. The variable is assigned a function. I'm sure this concept is not exclusive to AJAX, but that is the context I am using it in, if it makes a difference.
我有一个函数，里面有一个变量。变量被分配了一个函数。我确信这个概念不是 AJAX 独有的，但如果它有所不同，那就是我使用它的上下文。
function iClick(this)
{
var foo = "I would like to pass this.";
ajax.onreadystatechange = function (foo) { alert(foo); }
}
I want to pass a variable into the function. However, since there is no original function declaration, how do I specify parameters? Can I even do that?
我想将一个变量传递给函数。但是，由于没有原始函数声明，我该如何指定参数？我什至可以这样做吗？
回答by Nick Craver
Just don't declare that variable as a parameter in your anonymous function, like this:
只是不要在匿名函数中将该变量声明为参数，如下所示：
function iClick(this)
{
var foo = "I would like to pass this.";
ajax.onreadystatechange = function () { alert(foo); }
}
When you call the first parameter fooit's whatever's callingthat callback passes in that's fooinside the function. If you want to reference a previously declared variable just do that, make sure notto use a parameter with the same name.
当您调用第一个参数时，foo它是回调传入的函数内部的任何调用foo。如果您想引用先前声明的变量就这样做，请确保不要使用具有相同名称的参数。
回答by John Hartsock
You can create a function like this
您可以创建这样的函数
var c="hello";
(function(b){
alert(b)
})(c);
result would be "hello"
结果将是“你好”
回答by Claudiu
You can also do this, but maybe it's not necessary:
您也可以这样做，但也许没有必要：
function iClick(this)
{
var foo = "I would like to pass this.";
ajax.onreadystatechange = (function(thevar) {
return function () { alert(thevar); };
})(foo);
}
回答by Jo?o Pimentel Ferreira
As @John Hartsock referred, the answer that everyone should really remember is this
正如@John Hartsock 所提到的，每个人都应该真正记住的答案是这个
var c="hello";
(function(b){
alert(b)
})(c);
And that's very important for example in a forloop when there is some async function inside it, because otherwise you don't get the correct item.
这非常重要，例如在for循环中，当其中有一些异步函数时，否则您将无法获得正确的项目。
Tell me, what comes out from here?
告诉我，从这里出来的是什么？
for (var i=0; i<5; i++){
setTimeout(function(){
console.log(i);
}, 1000);
}Exactly: all 5, because when all the timers are triggered after 1 second, variable iis already at the value 5.
完全正确：全部 5 个，因为当所有计时器在 1 秒后触发时，变量i已经为值5。
But if you use a self-invoked anonymous function(SIAF) like this
但是如果你使用像这样的自调用匿名函数（SIAF）
for (var i=0; i<5; i++){
(function (j){
setTimeout(function(){
console.log(j);
}, 1000);
})(i);
}it does work, since every time the function is evoked, it runs another instance of the function and as any function, it has its own local variables. I do not merely define the function, I also run it right away (through the ();at the end), but then internally a new instance of the function will be created with different internal local variables, as I parse to the function a different variable every time I run it.
它确实有效，因为每次调用该函数时，它都会运行该函数的另一个实例，并且与任何函数一样，它都有自己的局部变量。我不仅定义了函数，我还立即运行它（通过();最后），但是然后在内部创建一个具有不同内部局部变量的函数的新实例，因为我每次解析到函数一个不同的变量时间我运行它。
回答by vittore
I belive you wanted something like that
我相信你想要那样的东西
function handleAjaxRequest(params) {
var context = {'b':'inner', 'c': params['c']};
function rendered(html) {
// render
}
function gotPart(part) {
context['a'] = part;
engine.render(context).addCallback(rendered);
}
ajax.getPart(params).addCallback(gotPart);
}
