In a standard web browser, which statement best describes how you can read and write files using JavaScript?

Introduction / Context:
File access is a sensitive topic in web security. While many programming environments allow direct reading and writing of local files, web browsers intentionally restrict what client side JavaScript can do. This question tests whether you understand that JavaScript running in the browser cannot freely access arbitrary files on the user machine and must use controlled, sandboxed mechanisms for any file related operations.

Given Data / Assumptions:

• We are discussing JavaScript running in a standard web browser, not in a server side environment.
• Users and security models must protect local file systems from web pages.
• Modern browsers provide limited file access through features such as input type file and the File API.
• Persistent storage is often handled via servers or sandboxed local storage APIs.

Concept / Approach:
Client side JavaScript operates inside a security sandbox. By default, it cannot open arbitrary paths on the user file system. To read a file, the user must explicitly select it, usually through an input element of type file or drag and drop. JavaScript can then use the File and FileReader APIs to read the chosen file content in memory. For writing data persistently, JavaScript can send data to a server using HTTP requests, or it can use browser controlled storage mechanisms such as localStorage, IndexedDB, or the File System Access API, which still require user consent and operate within strict limits. The key idea is that direct unrestricted file system access is not allowed for security reasons.

Step-by-Step Solution:
Step 1: Recognize that web browsers use a sandbox to protect the local file system from arbitrary web page access. Step 2: Recall that reading a file usually requires explicit user selection through a file input or similar mechanism. Step 3: Remember that writing files directly to arbitrary locations is not allowed; instead, developers use server side code or controlled storage APIs. Step 4: Choose the option that states JavaScript cannot directly read and write arbitrary local files and mentions controlled APIs and server communication.

Verification / Alternative check:
You can verify this by trying to open a local file path directly in a JavaScript function without any user input. Browsers do not allow such operations. Instead, tutorials on file handling in JavaScript always involve file inputs, drag and drop, or storage APIs with user permission. Furthermore, security guidelines for web development emphasize that file system operations should go through server side code or standardized sandboxed APIs, which aligns with option A.

Why Other Options Are Wrong:
Option B is wrong because unrestricted file access from web pages would be a major security risk. Option C is incorrect because even administrator rights do not grant the browser permission to bypass the sandbox model. Option D is wrong because JavaScript can read user selected files, and some sandboxed write mechanisms exist. Option E is clearly false because there is no standard writeFile function that writes directly to the operating system root directory.

Common Pitfalls:
Developers who are new to web security sometimes expect JavaScript to behave like desktop scripting languages and attempt to access local files directly. Another pitfall is misunderstanding the purpose of localStorage or IndexedDB and assuming they correspond to arbitrary file access. By remembering that client side JavaScript can only access files in tightly controlled ways, you will design safer web applications and choose the correct architecture for file handling tasks.

Final Answer:
Client side JavaScript cannot directly read and write arbitrary local files for security reasons; it can read selected files via controlled APIs such as the File API and must send data to a server or use sandboxed APIs for persistent storage