File handling is a common task in backend applications, from reading and writing files on the server to managing user file uploads. Node.js offers powerful tools to work with files efficiently. In this chapter, we will learn how to handle files and manage file uploads in Node.js using fs (file system) and multer.

Reading and Writing Files in Node.js

Node.js includes the fs module to work with the file system. This module allows you to perform operations such as reading, writing, deleting, and renaming files on the server. Let's see how to perform some of the most common operations.

Reading Files

To read the content of a file, we use the fs.readFile method. Here's an example:

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Writing Files

To write to a file, we can use fs.writeFile. If the file does not exist, it will be created; if it already exists, its content will be overwritten.

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Deleting Files

To delete a file, we use fs.unlink:

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File Upload in Node.js with Multer

multer is a middleware that makes managing file uploads in Node.js easier. With multer, we can handle files sent through HTML forms and store them on the server. First, let's install the package:

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Configuring Multer

To handle file uploads, we need to configure multer on our Express server. Let's see how to do it:

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Uploading Multiple Files

If we need to allow the uploading of several files at once, we can use upload.array() instead of upload.single():

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Custom Storage

Multer also allows configuring more advanced storage options like renaming files and defining where they will be stored. Let's see how to configure custom storage:

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Security Considerations for File Handling

File handling can introduce security vulnerabilities if proper measures are not taken. Here are some tips to improve security when handling files in Node.js:

• File type validation: Ensure you validate the file type users can upload to prevent the execution of malicious files.

• File size: Set a limit on the size of files users can upload to avoid overloading the server.

• File names: Generate unique names for uploaded files to avoid overwriting existing files.

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Summary

In this chapter, we learned how to handle files in Node.js using the fs module to read, write, and delete files, and how to manage file uploads using the multer middleware. These skills are fundamental for many modern applications, from image storage to document management.