20 interview questions on Javascript - Security by design for developers (2026)

Hard

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Which expression completes the code to ensure the absence of a prototype?

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Medium

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What is the behavior of this code when accessing proxy.name?

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Medium

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What is the most concise and robust pattern to access a potentially missing nested property and provide a default value?

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Medium

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What is displayed in the console after executing this code?

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Medium

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What is the fundamental difference between Object.freeze() and Object.seal() in JavaScript?

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Medium

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What is the main advantage of using structuredClone() compared to the JSON.parse(JSON.stringify(obj)) method?

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WeLoveDevsat Sep 15, 2026

Hard

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What is the architectural advantage of using WeakMap rather than Map to associate private data with DOM objects?

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Medium

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Why do browsers mandate the HTTPS protocol for registering Service Workers?

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Hard

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What is the output of this code?

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Medium

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What is the structural difference between encapsulation via a closure and via an ES module?

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Hard

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What is the correct syntax to invoke the sanitize function as a tagged template?

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Medium

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What is the recommended method for inserting text content from a user into the DOM to prevent XSS flaws?

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Hard

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What is the fundamental difference between Map and WeakMap regarding reference management?

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Easy

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Why is it preferable to use JSON.parse() rather than eval() to transform a string into an object?

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Hard

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What is the main risk associated with using this Map object?

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WeLoveDevsat Sep 15, 2026

Hard

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Which approach guarantees the encapsulation of private data in a class without exposing the properties on the instance?

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Easy

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Why ban the use of eval() in a secure application architecture?

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WeLoveDevsat Sep 15, 2026

Medium

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Identify the error in this code aiming to retrieve the value of the private field.

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Easy

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Why is it recommended to use Web Workers to process sensitive or complex data?

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WeLoveDevsat Sep 15, 2026

Hard

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Identify the logical error preventing this asynchronous function from working properly.

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WeLoveDevsat Sep 15, 2026

20 interview questions on Javascript - Security by designfor developers (2026)

Test your technical skills before an interview of Javascript - Security by design with 20 corrected questions. Beginner, Intermediate or Expert level.

Which expression completes the code to ensure the absence of a prototype?

What is the behavior of this code when accessing proxy.name?

What is the most concise and robust pattern to access a potentially missing nested property and provide a default value?

What is displayed in the console after executing this code?

What is the fundamental difference between Object.freeze() and Object.seal() in JavaScript?

What is the main advantage of using structuredClone() compared to the JSON.parse(JSON.stringify(obj)) method?

What is the architectural advantage of using WeakMap rather than Map to associate private data with DOM objects?

Why do browsers mandate the HTTPS protocol for registering Service Workers?

What is the output of this code?

What is the structural difference between encapsulation via a closure and via an ES module?

What is the correct syntax to invoke the sanitize function as a tagged template?

What is the recommended method for inserting text content from a user into the DOM to prevent XSS flaws?

What is the fundamental difference between Map and WeakMap regarding reference management?

Why is it preferable to use JSON.parse() rather than eval() to transform a string into an object?

What is the main risk associated with using this Map object?

Which approach guarantees the encapsulation of private data in a class without exposing the properties on the instance?

Why ban the use of eval() in a secure application architecture?

Identify the error in this code aiming to retrieve the value of the private field.

Why is it recommended to use Web Workers to process sensitive or complex data?

Identify the logical error preventing this asynchronous function from working properly.