Node.js fs.filehandle.fd() 方法

fs.filehandle.fd()方法是文件系统模块中fs.filehandle类的内置应用程序编程接口，用于提供此文件句柄对象的数字文件描述符。
句法：

const filehandle.fd()

参数：此方法不接受任何参数。
返回值：此方法返回此文件句柄对象的数字文件描述符。
下面的程序说明了 Node.js 中fs.filehandle.fd()方法的使用：
示例 1：文件名：index.js

javascript

// Node.js program to demonstrate the
// filehandle.fd() method
const fs = require('fs');
const fsPromises = fs.promises;
 
console.log("content of file before operation :- "
            + (fs.readFileSync('example.txt')));
 
// Initiating asyncrionise function
async function funct() {
 
    // Initializing filehandle
    let filehandle = null;
    let value = null;
 
    try {
 
        // Creating and initiating  filehandle
        filehandle = await
            fsPromises.open('example.txt', 'r+');
 
        // Getting the Numeric file descriptor
        // by using fd api
        value = filehandle.fd;
 
    } finally {
 
        if (filehandle) {
 
            // Close the file if it is opened.
            console.log(
                "Numeric file descriptor :- " + value);
            console.log(
                "content of file after operation :- " +
                (fs.readFileSync('example.txt')));
 
            await filehandle.close();
        }
    }
}
 
funct().catch(console.error);

运行程序前的目录结构：

运行程序后的目录结构：

使用以下命令运行index.js文件：

node index.js

输出：

content of file before operation :- ABCD
Numeric file descriptor :- 3
content of file after operation :- ABCD

示例 2：
文件名：index.js

javascript

// Node.js program to demonstrate the
// filehandle.fd() method
const fs = require('fs');
const fsPromises = fs.promises;
 
// Data for the new file
let data = "This is a file containing "
            + "a collection of books.";
 
// Name of the file to be created
let file = "books.txt";
 
// Creating the new file 'books.txt'
fs.writeFile(file, data, (err) => {
 
    // Catching error
    if (err) {
        console.log(err);
    }
});
 
// Using fs.exists() method
fs.exists(file, (exists) => {
    if (exists) {
        console.log("content of file "
            + "before operation :- "
            + (fs.readFileSync(file)));
    }
});
 
// Initiating asyncrionise function
async function funct() {
 
    // Initializing filehandle
    let filehandle = null;
 
    try {
 
        // Creating and initiating  filehandle
        filehandle = await
                fsPromises.open(file, 'r+');
 
        // Getting the Numeric file descriptor
        // by using fd api
        value = filehandle.fd;
 
    } finally {
 
        if (filehandle) {
 
            // Close the file if it is opened.
            console.log(
                "Numeric file descriptor :- "
                + value);
                 
            console.log("content of file "
                + "after operation :- "
                + (fs.readFileSync(file)));
 
            await filehandle.close();
        }
    }
}
 
funct().catch(console.error);

运行程序前的目录结构：

运行程序后的目录结构：

使用以下命令运行index.js文件：

node index.js

输出：

content of file before operation :- This is a file containing a collection of books.
Numeric file descriptor :- 4
content of file after operation :- This is a file containing a collection of books.

参考： https://nodejs.org/dist/latest-v12.x/docs/api/fs.html#fs_filehandle_fd