Testing, debugging, and performance optimization are essential skills for every JavaScript developer. They involve identifying and fixing errors, improving code quality, and ensuring applications run efficiently. Key topics include understanding testing tools like Jest and Mocha, debugging techniques using browser DevTools, and optimizing performance by reducing memory usage and improving execution speed. These concepts are important for building robust and user-friendly web applications. Interviewers often ask questions on these topics to assess a candidate’s problem-solving and optimization skills.
1.) What is the primary purpose of unit testing?
A) To test the entire application workflow.
B) To test individual components or functions.
C) To identify security vulnerabilities.
D) To measure application performance.
2.) Which tool is commonly used for JavaScript testing?
A) Babel
B) ESLint
C) Webpack
D) Jest
3.) Which of the following best describes load testing?
A) Testing an application for security vulnerabilities.
B) Measuring the application’s performance under high user load.
C) Testing individual components in isolation.
D) Debugging memory leaks in the code.
4.) What is the purpose of the Coverage tab in Chrome DevTools?
A) To identify unused CSS and JavaScript.
B) To measure network requests.
C) To display memory usage.
D) To debug event listeners.
5.) Which method in Chrome DevTools helps measure script execution time?
A) console.log()
B) console.time() and console.timeEnd()
C) performance.now()
D) debugger
6.) What is the purpose of using try…catch blocks in debugging?
A) To prevent syntax errors.
B) To catch and handle runtime errors gracefully.
C) To log error messages to the console.
D) To improve application performance.
7.) Which DevTools feature helps analyze how long each function takes to execute?
A) Console
B) Network tab
C) Performance tab
D) Application tab
8.) How can you monitor memory usage in a web application?
A) Using the Console tab in DevTools.
B) Using the Memory tab in DevTools.
C) By writing custom JavaScript functions.
D) By enabling verbose logging.
9.) Which of the following is a common cause of memory leaks in JavaScript?
A) Using const instead of var.
B) Unreferenced closures.
C) Event listeners not being removed.
D) Using arrow functions.
10.) What does console.assert() do in debugging?
A) Throws an error if the condition is false.
B) Stops code execution.
C) Logs all variable values.
D) Displays debugging information in a separate file.
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