Node.js脚本私有变量值不会被内部函数更改

Question

考虑以下简单脚本：

var sourcePath = 'src';
function setPath(path){
sourcePath = path || sourcePath;
return sourcePath;
}
console.log('sourcePath is ' + setPath('somepath') + ' from setPath.js calling the function');
console.log('sourcePath is ' + sourcePath + ' from setPath.js sourcePath vaue ');
exports.getCustomContextPath = setPath;
exports.sourcePath = sourcePath;

运行此脚本时，运行此脚本的输出符合预期：

sourcePath is somepath from setPath.js calling the function
sourcePath is somepath from setPath.js sourcePath value

如果我在测试器文件中导入相同的文件并像这样使用它：

const pathSetter = require('./setPath');
var test = pathSetter.getCustomContextPath('./temp/test');
console.log('the path set from test.js ' + test + " by calling getCustomContextPath function with '.temp/test'" )
console.log('the path set from test.js ' + pathSetter.sourcePath + " this is the sourcePath value after calling with '.temp/tr'" )
var test2 = pathSetter.getCustomContextPath();
console.log('the path set from test.js' + test2 + " by calling getCustomContextPath function with no parameter " )
console.log('the path set from test.js ' + pathSetter.sourcePath + " this is the sourcePath value after calling with no parameter")

我希望在调用函数时sourcePath变量的值会更改setPath但正如您在下面看到的，在打印出sourcePath的值时，它仍然设置为其默认值somePath。下面是运行测试脚本的输出：

sourcePath is somepath from setPath.js calling the function
sourcePath is somepath from setPath.js sourcePath value
the path set from test.js ./temp/test by calling getCustomContextPath function with '.temp/test'
the path set from test.js somepath this is the sourcePath value after calling with '.temp/tr'
the path set from test.js./temp/test by calling getCustomContextPath function with no parameters
the path set from test.js somepath this is the sourcePath value after calling with no parameters 

谁能告诉我为什么在我期望脚本函数更改它之后没有更改sourcePath的值，而只是当我从测试文件目录访问它而不是函数调用返回它时？

Answer 1

当你做exports.sourcePath = sourcePath;时，你是在做一个简单的分配。

var sourcePath不是指针。因此，它在导出时初始化为somepath并且永远不会更改。

如果要检索良好的 sourcePath 值，可以按exports.sourcePath = () => sourcePath;

Answer 2

exports.sourcePath = sourcePath;

这里sourcePath不是通过引用设置的。一旦你在export.sourcePath中导出了一个值，即使你改变全局变量">sourcePath"的值，它也不会改变;

考虑它就像你写的那样

export.sourcePath = "somepath";

现在它将如何改变，现在没有办法改变它。

您的困惑是，您将其设置为同一文件一次，但是在这种情况下，在执行exports.sourcePath之前，您将其值更改为"somePath"。

现在您可以尝试的是，尝试从第一个文件中删除这两行

console.log('sourcePath is ' + setPath('somepath') + ' from setPath.js calling the function');
console.log('sourcePath is ' + sourcePath + ' from setPath.js sourcePath vaue ');

然后尝试在不同的文件中打印其值。它将始终打印"src"。