node.js - 为什么在函数内部调用时这指向应用程序进程？

在Node应用程序中编写以下代码：

Date.prototype.getDayName = function() {
    let daysOfWeek = ['Sun','Mon','Tue','Wed','Thu','Fri','Sat']
    return daysOfWeek[this.getDay()]
}

(async () => {
    ...
    ...
    ...
})()

我得到this.getDay（）不是一个函数。当我在这种情况下登录时，我得到了过程对象：

    Object [global] {
global: [Circular],
process:
process {
    title: 'node',
    version: 'v10.12.0',
    versions:
    { http_parser: '2.8.1',
        node: '10.12.0',
        v8: '6.8.275.32-node.35',
        uv: '1.23.2',
        zlib: '1.2.11',
        ares: '1.14.0',
        .....
        .....
        .....

最佳答案

在编写自调用异步函数之前，您始终需要输入分号。该代码将像这样工作：

Date.prototype.getDayName = function() {
    let daysOfWeek = ['Sun','Mon','Tue','Wed','Thu','Fri','Sat']
    return daysOfWeek[this.getDay()]
}; //You need to put a semi-colon before writing a self calling async function

(async () => {
    ...
    ...
    ...
})()