如何操作 Node.js 中带有承诺的基于回调的 fs.readdir()方法？
原文:https://www . geesforgeks . org/操作方法-基于回调的-fs-readdir-带节点承诺的方法-js/
fs.readdir() 方法是在 Node.js 的 File System 模块中定义的，File System 模块基本上就是和用户电脑的硬盘进行交互。readdir()方法用于读取目录的内容。
fs.readdir()方法基于回调。使用回调方法导致回调嵌套或回调地狱问题的可能性很大。因此，为了避免这种情况，我们几乎总是喜欢使用基于承诺的方法。使用一些额外的 node.js 方法，我们可以用 promise 方式操作一个基于回调的方法。
语法:
fs.readdir(path, options)
注意:不需要回调，因为我们是用承诺的方式操作的。
参数:该方法接受两个参数，如上所述，如下所述:
- 路径:它是一个字符串、缓冲区或 url，用于指定目录的路径，我们尝试读取该目录的内容。
- 选项:是可选参数，这里我们指定编码技术(默认-utf8)等。
方法:基于回调的 fs.readdir()方法。为了用承诺来操作它，首先，我们使用在实用程序模块中定义的 promisify()方法将其转换为基于承诺的方法。
示例 1: 文件名:index.js
// Program to read file and folders of
// the current working directory
// Importing File System and Utilities module
const fs = require('fs')
const util = require('util')
// Convert callback based methods to promise
// based methods
const readDir = util.promisify(fs.readdir)
// Reading current working directory
readDir(process.cwd())
// If promise resolved and datas are fetched
.then(filenames => {
for(let filename of filenames) {
console.log(filename)
}
})
// If promise is rejected
.catch(err => {
console.log(`Error occurs,
Error code -> ${err.code},
Error No -> ${err.errno} `);
})
使用异步等待实现相同的功能:
// Program to read file and folders of the
// current working directory
// Importing File System and Utilities module
const fs = require('fs')
const util = require('util')
// Convert callback based methods to promise
// based methods
const readDir = util.promisify(fs.readdir)
const readDirectory = async (path) => {
const filenames = await readDir(path)
for(let filename of filenames){
console.log(filename)
}
}
readDirectory(process.cwd())
// If promise is rejected
.catch(err => {
console.log(`Error occurs,
Error code -> ${err.code},
Error No -> ${err.errno}`);
})
使用以下命令运行 index.js 文件:
node index.js
输出:
示例 2: 文件名:index.js
// Program to read file and folders of the
// current working directory or as the path
// given by command line argument
// Importing File System and Utilities module
const fs = require('fs')
const util = require('util')
// Convert callback based methods to promise
// based methods
const readDir = util.promisify(fs.readdir)
// The process.cwd() gives current working directory
const targetDir = process.argv[2] || process.cwd()
readDir(targetDir)
// If promise resolved and datas are fetched
.then(filenames => {
for(let filename of filenames) {
console.log(filename)
}
})
// If promise is rejected
.catch(err => {
console.log(err)
})
使用异步等待实现相同的功能:
// Program to read file and folders of the
// current working directory or as the path
// given by command line argument
// Importing File System and Utilities module
const fs = require('fs')
const util = require('util')
// The process.cwd() gives current working directory
const targetDir = process.argv[2] || process.cwd()
// Convert callback based methods to promise
// based methods
const readDir = util.promisify(fs.readdir)
const readDirectory = async (path) => {
const filenames = await readDir(path)
for(let filename of filenames){
console.log(filename)
}
}
readDirectory(targetDir)
// If promise is rejected
.catch(err => {
console.log(`Error occurs,
Error code -> ${err.code},
Error No -> ${err.errno}`);
})
使用以下命令运行 index.js 文件:
node index.js
输出:
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