[英]Node.js script private variable value is not changed by the internal function
考慮以下簡單腳本:
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;
運行該腳本時,其輸出符合預期:
sourcePath is somepath from setPath.js calling the function
sourcePath is somepath from setPath.js sourcePath value
如果我將同一文件導入測試器文件並按如下方式使用它:
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")
我希望在調用setPath
函數時可以更改sourcePath
變量的值,但是如下所示,當打印出sourcePath
的值時,它仍設置為其默認值somePath
。 這是運行測試腳本的輸出:
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
誰能告訴我為什么在我期望腳本函數對其進行更改之后,但僅當我從測試文件目錄訪問它而不是函數調用返回它時,才更改sourcePath
的值嗎?
當您執行exports.sourcePath = sourcePath;
您正在進行簡單的分配。
var sourcePath
不是指針。 因此它在導出時被初始化為somepath
並且永不改變。
如果要檢索良好的sourcePath值,可以將其作為exports.sourcePath = () => sourcePath;
exports.sourcePath = sourcePath;
這里sourcePath並非通過引用設置。 一旦在exports.sourcePath中導出了一個值,即使您更改了全局變量“ sourcePath ”的值,該值也不會更改。
就像你寫的那樣考慮
Exports.sourcePath =“ somepath”;
現在它將如何改變,現在沒有辦法改變它。
你的困惑是,你設置它,一旦它同一個文件,但在這種情況下,執行exports.sourcePath之前,你改變了它的價值,以“somePath”。
現在您可以嘗試的是,嘗試從第一個文件中刪除這兩行
console.log('sourcePath is ' + setPath('somepath') + ' from setPath.js calling the function');
console.log('sourcePath is ' + sourcePath + ' from setPath.js sourcePath vaue ');
然后嘗試在其他文件中打印其值。 它將始終打印“ src”。
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