[Solved] Consider this code snippet in main.ts:import helmet from 'helmet'; app.use(helmet);What is the issue with this middleware usage? | NestJS

NestJS - Middleware

Consider this code snippet in main.ts:

import helmet from 'helmet';
app.use(helmet);

What is the issue with this middleware usage?

AHelmet requires additional configuration options to work

BHelmet is imported incorrectly and will cause a runtime error

CHelmet middleware should be applied after app.listen()

DHelmet middleware is not invoked as a function, so no middleware is applied

Step-by-Step Solution

Solution:

Step 1: Understand Helmet usage
Helmet exports a function that returns middleware, so it must be called.
Step 2: Identify the problem
Using app.use(helmet); passes the function itself, not the middleware it returns.
Step 3: Correct usage
Use app.use(helmet()); to apply the middleware properly.
Final Answer:
Helmet middleware is not invoked as a function, so no middleware is applied -> Option D
Quick Check:
Middleware functions must be invoked before passing to app.use() [OK]

Quick Trick: Call helmet() to get middleware before app.use() [OK]

Common Mistakes:

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