node . js fspromises . appendfile()函数
原文:https://www . geesforgeks . org/node-js-fspromiss-append file-function/
fsPromises.appendFile() 方法用于将给定数据异步追加到文件中。如果新文件不存在，则会创建一个新文件。options 参数可用于修改操作的行为。
语法:
fsPromises.appendFile( path, data, options )
参数:该方法接受三个参数，如上所述，如下所述:
- Path: It is a string, buffer, web address or number, which indicates the name of the source file or the file descriptor to be attached.
- Data: is a character string or buffer that indicates the data that must be appended.
- Option: is a string or object that can be used to specify optional parameters that affect output. It has three optional parameters:
- Code: is a string that specifies the file code. The default value is utf8.
- Mode: An integer that specifies the file mode. The default value is "0fso666".
- Flag: It is a string that specifies the flag to be used when attaching to a file. The default value is "A".
返回值:返回承诺。
示例:本示例使用名为“example_file”的示例 txt 文件，其中包含 Hello 文本。
文件名:index.js
// Node.js program to demonstrate the
// fsPromises.appendFile() method
// Import the filesystem module
const fs = require('fs');
const fsPromises = fs.promises;
// Get the file contents before the append operation
console.log("\nFile Contents of file before append:",
fs.readFileSync("example_file.txt", "utf8"));
fsPromises.appendFile("example_file.txt", "GeeksforGeeks")
.then(function(){
console.log("\nFile Contents of file after append:",
fs.readFileSync("example_file.txt", "utf8"))
})
.catch( function (err) { console.log(err); });
注意:用下面的命令运行 index.js 文件:
node index.js
输出:
File Contents of file before append: Hello
File Contents of file after append: HelloGeeksforGeeks
注意:如果选项是字符串，则指定编码。该路径可以被指定为一个文件句柄，该文件句柄已经被打开以进行附加(使用 fsPromises.open() )。
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