Node.js fs.filehandle.write()方法
原文:https://www . geesforgeks . org/node-js-fs-file handle-write-method/
fs.filehandle.write() 方法是文件系统模块中类 fs.filehandle 的内置应用程序编程接口，用于将缓冲区中的数据写入该特定文件。 语法:
const filehandle.write(buffer[, offset[, length[, position]]])
参数:该方法取以下参数:
- 缓冲器:提供需要存储的数据的缓冲器。
- 偏移量:缓冲区中的起点。
- 长度:要写入的字节数。
- 位置:文件的开始点。
返回值:该方法返回一个待定承诺，该承诺包含缓冲区和描述写入字节数的 bytesWritten 属性。 下面的程序说明了 fs.filehandle.write() 方法在 Node.js: 中的使用示例 1: 文件名:index.js
java 描述语言
// Node.js program to demonstrate the
// filehandle.write() method
const fs = require('fs');
const fsPromises = fs.promises;
console.log("file before write operation :- "
+ fs.readFileSync('example.txt', 'utf8'));
// Initiating asyncrionise function
async function funct() {
// Initializing following variables
let filehandle = null;
let prom = null;
let buffer = Buffer.from('Geeks');
try {
// Creating and initiating filehandle
filehandle = await
fsPromises.open('example.txt', 'r+');
// Writting the file by using
// write() method
prom = filehandle.write(
buffer, 0, buffer.length, 0);
} finally {
if (filehandle) {
// Display the result
prom.then(function (result) {
console.log(
"file after write operation :- "
+ (result.buffer).toString());
})
// Close the file if it is opened.
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:
file before write operation :- Geeks for Geeks
file after write operation :- Geeks
示例 2: 文件名:index.js
java 描述语言
// Node.js program to demonstrate the
// filehandle.sync() 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) => {
// Cathing 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;
// Initializing following variables
let buffer = Buffer.from('ABCD');
try {
// Creating and initiating filehandle
filehandle = await
fsPromises.open(file, 'r+');
// Writting the file
// by using write() method
prom = filehandle.write(
buffer, 0, buffer.length, 0);
} finally {
if (filehandle) {
// Display the result
prom.then(function (result) {
console.log(
"file after write operation :- "
+ (result.buffer).toString());
})
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.
file after write operation :- ABCD
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