javascript - 从函数返回并重新声明变量

Question

在为我的入门编程课做作业时，我创建了一个函数，并在一些人的帮助下一切都正常工作(顺便说一句，非常感谢)，现在我遇到了一个新问题。我有两个变量，在启动函数之前声明并提示输入值，如果未通过，则提示输入新值。但现在当我返回它们时，它不会更改代码之外的变量。

// 1 Declare Variables
var numTrees;
var counter = 0;
var answer = "no";

function treeFunction(answer, counter, numTrees) {
while (answer == "no" && counter < 3)
{
    if (numTrees < 5 || numTrees > 10)
    {
        alert("That is an incorrect value.\nThe sample size should be less than 5 or greater than 10.\nPlease try again.");
        answer = "no";
        numTrees = prompt("Please reenter the amount of trees in your sample.");
        alert("You have entered: " + numTrees)
        counter + 1;
    }
    else 
    {
        answer = "yes";
    }
}
if (answer == "no") {
    alert("You have entered an incorrect number too many times.\nThe Program will now end.");
    window.open('', '_self', '');
    window.close();
} else if (answer == "yes") {
    return numTrees;
}
}
// 2 Prompt the Instructor for the number of Trees
numTrees = prompt("How many trees are in your sample?");
alert("You have entered: " + numTrees);
treeFunction(answer, counter, numTrees)
document.write(numTrees); 
document.write("<br/>")
document.write("<br/> <br/>" + "End of Program.");

编辑:我改变了我正在做的事情，我不再需要返回两个变量，只返回 numTrees。然而，由于某种原因， document.write 显示原始值，而不是在返回后在函数中更改为的值。

Answer 1

answer、counter、numTrees 是全局的，但是当您将它们作为参数传递给函数时；

function treeFunction(answer, counter, numTrees) {

您将获得一组新的局部变量，它们恰好与全局变量同名，因此隐藏它们。

要使用全局变量，请勿传递它们

function treeFunction() {
   answer = ....

(您还希望 counter += 1 实际递增变量)