Javascript：打印出数组的索引
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Javascript: print out index of an array
提问by hvu89
I have this question in an interview
我在面试中有这个问题
Using javascript, write an array of n elements. Each element in the array is a function that calls console.log of its own index. For eg, the first element will console.log 0, second element will console.log 1....
使用 javascript，编写一个包含 n 个元素的数组。数组中的每个元素都是一个调用自己索引的 console.log 的函数。例如，第一个元素是 console.log 0，第二个元素是 console.log 1....
Thanks in advance
提前致谢
Edit: Sorry for asking before researching. Im new to programming & dont know what closure is & couldnt find something in search. I got the answer myself but here is the problem I had. I wrote something like this
编辑：抱歉在研究之前询问。我是编程新手，不知道闭包是什么，在搜索中找不到东西。我自己得到了答案，但这是我遇到的问题。我写了这样的东西
n = 10
var array = []
for (var i=0; i < n; i ++) {
array[i] = function() {
console.log(i);
}
}
for (var j=0; j < n; j ++) {
array[j]()
}
回答by jfriend00
There isn't an easy way to do what you're asking because if you put a function in each array element, that function wouldn't know what it's array index was unless you somehow bound a custom function for each array index.
没有一种简单的方法可以完成您的要求，因为如果您在每个数组元素中放置一个函数，该函数将不知道它的数组索引是什么，除非您以某种方式为每个数组索引绑定了一个自定义函数。
But, all of this sounds a little like you're not telling us what the real problem is. If you're iterating over an array and calling a function in the array element, then just pass the index to that function as the first argument.
但是，所有这些听起来有点像您没有告诉我们真正的问题是什么。如果您要遍历数组并在数组元素中调用函数，则只需将索引作为第一个参数传递给该函数。
You could call each function in the array and pass it the index of its slot like this:
您可以调用数组中的每个函数并将其插槽的索引传递给它，如下所示：
function fn1(index) {
console.log(index);
// do other things here specific to this function
}
// fn2 ... fn4 definitions
var listOfFunctions = [fn1, fn2, fn3, fn4];
for (var i = 0; i < listOfFunctions.length; i++) {
listOfFunctions[i](i);
}
Or, tell us what the real problem is so we can more directly help solve that.
或者，告诉我们真正的问题是什么，以便我们可以更直接地帮助解决这个问题。
回答by basilikum
Here is one (of multiple ways) to do it.
这是一种（多种方式）来做到这一点。
var arr = [];
for (var i = 0; i < 10; i++) {
arr.push(function(){
console.log(this.indexOf(arguments.callee));
});
}
arr[3](); //3
arr[7](); //7
thiswill refer to the array, if you call your function in the way arr[index](). arguments.calleerefers to the function itself, inside of itself. So the function searches itself inside of the array that it is attached to and prints out the found index.
this将引用数组，如果您以方式调用您的函数arr[index]()。arguments.callee指的是函数本身，在其内部。因此该函数在它所连接的数组内部搜索自身并打印出找到的索引。
EDIT
编辑
As jfriend00 pointed out correnctly, arguments.calleeis deprecated and is not supported in strict mode.
So here is a "cleaner" solution (with suggestion from Bergi):
正如 jfriend00 正确指出的那样，arguments.callee不推荐使用并且在严格模式下不受支持。所以这是一个“更清洁”的解决方案（来自贝尔吉的建议）：
var arr = [], func;
for (var i = 0; i < 10; i++) {
arr.push(function printIndex(){
console.log(this.indexOf(printIndex));
});
}
arr[3](); //3
arr[7](); //7
