Node.js this.varaiable 分配在 VS Code 中不起作用 [重复]

问：

如果我在其他地方运行它，则在 Node.js 代码下方运行它效果很好，但在 VS Code 中它会抛出错误。

    this.k= 8             
    TypeError: Cannot set properties of undefined (setting 'k')
    at subfun (file:///c:/Users/Administrator/Documents/2.js:3:15)
    at mainfun (file:///c:/Users/Administrator/Documents/2.js:6:5)
    at file:///c:/Users/Administrator/Documents/2.js:8:1
    at ModuleJob.run (node:internal/modules/esm/module_job:193:25)
    at async Promise.all (index 0)
    at async ESMLoader.import (node:internal/modules/esm/loader:530:24)
    at async loadESM (node:internal/process/esm_loader:91:5)
    at async handleMainPromise (node:internal/modules/run_main:65:12)

我的代码：

var mainfun = function (){
    function subfun(a){
        this.k= 8
        console.log(this.k)
    }
    subfun()
}
mainfun()

需要上述解决方案才能在 VS Code 上运行，我正在寻找错误原因。