High Security Question 205 of 226

How do you prevent XSS in a MERN app?

MERN Full Stack · Speak this in 60–90 seconds · Faridabad & Delhi NCR

The model does not read letters like humans. It reads these pieces, then predicts the next one.

I escape output, avoid dangerouslySetInnerHTML, and sanitize any rich text.

Why interviewers care about Security:

This is a process

question about Security.

Panels listen for order,

trade-offs, and what you would actually do on a Full Stack project - not buzzwords.

Stay structured

Name the idea, why it exists, then one short example.

Close cleanly

End with when you use it and one common pitfall.

Before the model can read a sentence, it goes through these steps:

1
I escape output, avoid
dangerouslySetInnerHTML, and sanitize any rich text.
2
HttpOnly cookies reduce token
theft from XSS.
3
Embeddings
Content-Security-Policy adds defense in depth.
4
Context mix
Attention looks at nearby tokens together.
5
Next token
The model scores what should come next.
6
Decode
IDs turn back into readable text.

Let's see how a real sentence is tokenized (tokens may vary by model):

Input text

“HttpOnly cookies reduce token theft from XSS.”

Tokenized output

HttpOnlycookiesreducetokentheftfrom

Token IDs (example)

2987408337471632900

Note: Actual tokens and IDs depend on the tokenizer (e.g., GPT, Llama, etc.).

I escape output, avoid dangerouslySetInnerHTML, and sanitize any rich text. HttpOnly cookies reduce token theft from XSS.