I/O operations like reading or writing a file is not possible with client-side javascript. However , this can be done by coding a Java applet that reads files for the script.
In JavaScript, you can read and write files using various methods, depending on whether you’re working on the client-side (browser) or the server-side (Node.js). Here’s how you can perform file operations in both scenarios:
Client-Side (Browser) using FileReader and Blob:
// Reading a file
function readFile(input) {
const file = input.files[0];
const reader = new FileReader();
reader.onload = function(event) {
const contents = event.target.result;
console.log("File contents:", contents);
// Do something with the file contents
};
reader.onerror = function(event) {
console.error("File could not be read! Code " + event.target.error.code);
};
reader.readAsText(file);
}
// Writing a file (client-side doesn't allow direct file writes for security reasons)
function writeFile(data, filename) {
const blob = new Blob([data], { type: "text/plain" });
const url = window.URL.createObjectURL(blob);
const a = document.createElement("a");
a.href = url;
a.download = filename;
a.click();
window.URL.revokeObjectURL(url);
}
Server-Side (Node.js) using fs module:
const fs = require('fs');
// Reading a file
fs.readFile('file.txt', 'utf8', (err, data) => {
if (err) {
console.error("Error reading file:", err);
return;
}
console.log("File contents:", data);
// Do something with the file contents
});
// Writing a file
const content = "Hello, this is a file content!";
fs.writeFile('newFile.txt', content, (err) => {
if (err) {
console.error("Error writing file:", err);
return;
}
console.log("File written successfully!");
});
Remember, when working on the client-side, you typically handle file inputs through user interactions, like selecting a file through an <input type="file"> element. On the server-side, you have direct access to the file system, so you can read from and write to files more freely.