Panel-ready MERN Full Stack questions for freshers and experienced developers. Practice at Coding Cadre in Faridabad, or Online from Delhi NCR.
A component is a function that returns UI from props and state.
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The virtual DOM is React's in-memory tree of UI.
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Class components use this.state and lifecycle methods.
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key helps React identify which item changed, was added, or was removed.
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Authentication proves who the user is, usually with a password, OTP, or OAuth login.
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A JSON Web Token is a signed string with a header, payload, and signature.
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Hashing turns a password into a one-way digest so a database leak does not reveal real passwords.
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The React form posts credentials to Express.
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HTTP-only cookies are harder for stolen scripts to read because JavaScript cannot access them.
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You build React into static files, run the Node API as a long-lived process, and put both on a public URL.
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Development builds include source maps, hot reload, and extra warnings.
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Staging is a production-like environment used to test a release before customers see it.
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PM2 keeps a Node process running, restarts it on crash, and can run multiple instances.
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Unit tests check one function or component in isolation.
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Jest is a JavaScript test runner for React components and Node unit tests.
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An assertion checks that actual output matches what you expect, such as a 200 status or a rendered heading.
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API tests lock in status codes, validation, and auth rules so refactors do not silently break the React client.
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CORS is a browser rule that blocks a page on one origin from reading another origin unless the server allows it.
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Cross-site scripting injects malicious JavaScript into a page other users load.
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API keys, database URIs, and JWT secrets in Git history can be cloned or leaked forever.
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