In web development, which of the following actions cannot be performed directly by client side JavaScript running in a browser for security reasons?

Introduction / Context:
Client side JavaScript runs inside the user's browser and is limited by security rules called the same origin policy and sandboxing. While JavaScript can do many interactive tasks on web pages, it cannot directly access server resources such as database files without going through server side code. This question tests whether you can distinguish between tasks that are possible in client side scripts and those that require server side support.

Given Data / Assumptions:

• JavaScript here refers to code executed in a browser, not Node.js on the server.
• The environment follows normal web security practices.
• We consider common operations around HTML forms and data storage.

Concept / Approach:
Client side JavaScript can read form values, validate them, show error messages and send data to the server using form submission or asynchronous requests. However, it cannot open or write to files on the server or manipulate the database directly. That responsibility belongs to server side technologies such as PHP, Java, Python or Node.js with appropriate database drivers. The correct option therefore must describe an action that would require direct server file or database access without server side code, which is not allowed from pure client side scripts.

Step-by-Step Solution:
Step 1: Check each option to see whether it involves only browser side activity or direct server side file or database access.Step 2: Option A describes sending form contents to a server side script, which is possible via form submission or fetch or Ajax.Step 3: Option C and option D describe validation and displaying error messages, which are classic use cases for client side JavaScript.Step 4: Option B talks about directly storing form contents into a database file on the server with no server side code, which is not possible because browser scripts cannot open server database files.Step 5: Therefore, option B is the correct answer because it describes something client side JavaScript cannot do.

Verification / Alternative check:
If client side scripts could write directly to server databases, any third party page or attacker could tamper with data simply by running JavaScript in a browser, which would be a serious security hole. Instead, all database operations must pass through authenticated server side logic. Documentation for web security emphasises that JavaScript in the browser can only communicate with the server over HTTP or HTTPS and cannot bypass server side protections. Option B violates this rule and is therefore impossible for pure client side code.

Why Other Options Are Wrong:
Option A is possible because sending data to the server is exactly what forms and asynchronous requests are designed to do. Option C is a standard practice where JavaScript checks field formats before submission. Option D is also a common behaviour where scripts update the page dynamically to show error messages or hints.

Common Pitfalls:
Beginners sometimes think that because JavaScript can send data to the server, it is directly writing to the database. In reality, the server decides what to do with the data. Another mistake is confusing client side JavaScript with server side JavaScript environments. When answering such questions, always think about where the code runs and what resources it can and cannot access.

Final Answer:
Directly storing a form's contents into a database file on the server without any server side code.