Directory
1. Conceptual understanding
2. Read the contents of the specified file
2.1, Example 1: read file
2.2. Example 2: Judging whether the file is read successfully
3. Write to the file
3.1 Examples:
3.2, Example 4: Judging whether the writing is successful
4. The problem of fs module-route dynamic splicing
4.1. Solution 1: Provide the full path
4.2. Solution 2: Use __dirname
4.3, code demo
5. Practical exercises: Examination results arrangement
5.1. Requirements:
5.2. Steps:
1. Concept understanding
Definition: The fs module is a module officially provided by Node.js for operating files. It provides a series of methods and properties to meet the needs of users for file operations.
Two important methods:
-
The fs.readFile() method is used to read the contents of the specified file
-
The fs.writeFile() method is used to write content to the specified file
const fs=require('fs')
Second, read the content in the specified file
2.1, Example 1: Read file
// 1. Import fs module to operate files, use fs to accept fs module
const fs = require('fs');
// After reading successfully
//2. Call the fs.readFile() method to read the file
// Parameter 1: The storage path of the read file
// Parameter 2: The encoding format is used to read the file, and utf-8 is generally specified by default
// Parameter 3: Callback function to get the results of read failure and success err (failed result) dataStr (successful result)
fs.readFile('./files/11.txt','utf-8', function(err,dataStr){
// 2.1 Print the failed result
// If the read is successful, the value of err is null
// If the reading fails, the value of err is an error object, and the value of dataStr is undefined
console. log(err);
console.log('-----');
// 2.2 Print the successful result
console.log(dataStr);
})
Run result:
2.2, Example 2: Judging whether the file is read successfully
Judging by the value of err
const fs = require('fs');
fs.readFile('./files/11.txt','utf-8', function(err,dataStr){
if(err){
return console.log('Failed to read file' + err.message)
}
console.log('read file successfully' + dataStr);
})
Run result:
3. Write to file
3.1 instance:
// 1. Import fs file system module
const fs = require('fs')
//2. Call the fs.writeFile() method to write the contents of the file
// Parameter 1: Indicates the storage path of the file
// Parameter 2: Indicates the content to be written
// parameter 3: callback function
fs.writeFile('./files/11.txt','hello node.js', function(err){
//2.1 If the file is written successfully, the value of err is equal to null
// 2.2 If the file write fails, the value of err is equal to an error object
console. log(err);
})
Run result:
3.2, Example 4: Judging whether the writing is successful
// 1. Import fs file system module
const fs = require('fs')
//2. Call the fs.writeFile() method to write the contents of the file
// Parameter 1: Indicates the storage path of the file
// Parameter 2: Indicates the content to be written
// parameter 3: callback function
fs.writeFile('./files/11.txt','hello node.js', function(err){
//2.1 If the file is written successfully, the value of err is equal to null
// 2.2 If the file write fails, the value of err is equal to an error object
// console. log(err);
//Check if the file was successfully written
if (err) {
return console.log("Failed to read file" + err.message);
}
console.log("read file successfully");
})
operation result:
Four, fs module-routing dynamic splicing problem
When using the fs module to operate files, if the provided operation path is a relative path starting with / or ../, it is easy to have the problem of path dynamic splicing error. Reason: When the code is running, it will execute the node command The directory where it is located, and the full path of the operated file is dynamically spliced.
4.1, Solution 1: Provide the full path
When using the fs module to operate files, provide the complete path directly, and do not provide a relative path starting with / or .., so as to prevent the problem of dynamic path splicing.
4.2, solution 2: use __dirname
__dirname indicates the directory where the current file is located and then character splicing
4.3, Code Demonstration
//Original method
const fs = require("fs");
fs.readFile("./files/11.txt", "utf-8", function (err, dataStr) {
if (err) {
return console.log("Failed to read file" + err.message);
}
console.log("read file successfully" + dataStr);
});
//Improve the method to provide a complete file storage path
// Pay attention to use the escape character \ otherwise the path cannot be read
const fs = require("fs");
fs.readFile("E: front end\\
odejsketangwangke\fs file system module\files\11.txt",
"utf-8",
function (err, dataStr) {
if (err) {
return console.log("Failed to read file" + err.message);
}
console.log("read file successfully" + dataStr);
}
);
//Improvement method 2: __dirname indicates the directory where the current file is located, and then character splicing
const fs = require("fs");
fs.readFile(__dirname + "./files/11.txt","utf-8",function (err, dataStr) {
if (err) {
return console.log("Failed to read file" + err.message);
}
console.log("read file successfully" + dataStr);
}
);
5. Practical practice: exam results arrangement
5.1, Requirement:
5.2, step:
5.3, code implementation
// 1. Import fs module to operate files, use fs to accept fs module
const fs = require("fs");
//2. Call the fs.readFile() method to read the file
fs.readFile("./files/chengj.txt", "utf-8", function (err, dataStr) {
// 3. Determine whether the read is successful
if (err) {
return console.log("Failed to read" + err.message);
}
// else {
// // return console.log("read successfully" + dataStr);
// }
// 4.1 first divide the results and data according to spaces
const arrOld = dataStr. split(" ");
console.log(arrOld);
// 4.2 Loop through the split array, and perform a string replacement operation on each item of data
const arrNew = [];
// For each item of data, replace the equal sign with a colon
arrOld.forEach((item) => {
arrNew.push(item.replace("=", ":"));
});
// 4.3 Merge each item in the new array to get a new string
const newStr=arrNew.join('\r\\
')
console. log(newStr);
// 5. Call the fs.writeFile() method to write the processed results into a new file
fs.writeFile('./files/chengji-ok.txt', newStr, function(err){
if(err){
return console.log('Failed to write file!' + err.message);
}
console.log('scores written successfully!');
})
});
The knowledge points of the article match the official knowledge files, and you can further learn relevant knowledge. Vue entry skill tree Node.js and npmNode installation and configuration