Javascript for 循环索引变量成为全局范围的一部分？
也许我不知道 for 循环索引变量如何确定作用域，但当我的一个循环没有完成时，我感到非常惊讶，似乎是因为从循环内调用的函数包含一个 i 也是其 for 循环索引。
下面是我整理的一个小脚本来演示此行为：
var loopOne = function(test) {
for(i = 0; i < test.length; i++)
console.log(getMask(test));
};
var getMask = function(pass) {
var s = "";
for (i = 0; i < pass.length; i++) {
s = s + "*";
}
return s;
};
loopOne('hello');
如果我在 Chrome 中运行此脚本并查看控制台日志，我应该会看到 ***** 五次。不过，我只见过一次。经过进一步检查，如果我在 Chrome javascript 控制台中输入 i，它将输出 6 (= 'hello'.length + 1)。这让我认为 i 已经成为全局范围的一部分，并且不限于需要它的 for 循环的范围。
这是正确的吗？如果是这样，在 JavaScript 中定义 for 循环的索引变量的更好做法是什么？
Perhaps I'm not aware of how for loop index variables get scoped, but I was very surprised when one of my loops didn't complete, seemingly because a function called from within a loop contained an i for its for loop index as well.
Here's a little script I put together to demonstrate this behavior:
var loopOne = function(test) {
for(i = 0; i < test.length; i++)
console.log(getMask(test));
};
var getMask = function(pass) {
var s = "";
for (i = 0; i < pass.length; i++) {
s = s + "*";
}
return s;
};
loopOne('hello');
If I run this in Chrome and look at the console log, I should see ***** five times. However, I only see it once. Upon further inspection, if I type i in the Chrome javascript console, it will output 6 ( = 'hello'.length + 1). This makes me think that i has become a part of the global scope and is not limited to the scope of the for loop for which it was needed.
Is this correct? If so, what's a better practice for defining the index variable of a for loop in javascript?
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在 Javascript 中，变量的作用域是
var关键字。当使用var声明变量时，变量的作用域为当前函数。当不使用var关键字分配给变量时，假定您正在谈论相同或更高范围内已定义的变量。如果没有找到，则在最高范围内创建该变量。底线：使用
var声明所有变量。In Javascript, variables are scoped with the
varkeyword. When declaring variables withvar, the variable is scoped to the current function. When assigning to a variable without using thevarkeyword, it is assumed you're talking about an already defined variable in the same or a higher scope. If none is found, the variable is created in the highest scope.Bottom line: declare all your variables using
var.您应该使用
let声明循环索引变量：这将为变量声明并设置正确的范围。
You should declare your loop index variable with
let:That will declare and set the proper scope for the variable.
当您使用
var声明变量时，您将它们的范围限定为当前执行上下文。如果不这样做，它们将成为全局对象（浏览器中的
window）的属性。When you declare your variables with
var, you scope them to the current execution context.When you don't, they become properties of the global object (
windowin a browser).