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JavaScript Skill Exam

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1. How can you handle circular references in JavaScript when working with complex data structures?

Option: By avoiding nested objects and arrays.

Option: Using weak references that can be garbage collected independently.

Option: Manually breaking circular references by setting properties to null.

Option: Circular references are not a problem in JavaScript.

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2. Explain the concept of reactive programming in JavaScript and its use cases.

Option: A programming paradigm based on data streams and propagating changes automatically.

Option: Related to asynchronous programming with promises.

Option: A way to manage complex state in applications.

Option: Not a widely used concept in JavaScript. (Requires libraries like RxJS)

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3. What is the syntax for creating a new instance of a class in JavaScript (assuming classes are defined)?

Option: var objectName = new ClassName(parameters);

Option: define objectName = ClassName(parameters);

Option: create objectName = ClassName(parameters);

Option: ClassNam objectName(parameters);

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4. What is the difference between strict mode and non-strict mode in JavaScript?

Option: Strict mode enforces stricter coding practices and catches potential errors.

Option: Strict mode is only used for server-side JavaScript.

Option: Strict mode is slower than non-strict mode.

Option: There is no practical difference.

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5. What is the purpose of the async/await syntax in JavaScript?

Option: To define asynchronous functions and handle promises more easily.

Option: To create multi-threaded applications.

Option: To improve performance of synchronous code.

Option: To define event listeners.

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6. How can you achieve immutability in JavaScript objects?

Option: By defining constants using const. (This prevents reassignment of the reference, but nested objects can still be modified)

Option: By using libraries like Immutable.js.

Option: By recursively freezing all nested objects within the main object.

Option: Immutability is not possible in JavaScript.

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7. How do you select all elements with the class name "myClass" in the DOM using JavaScript?

Option: document.getElementsByClass("myClass")

Option: document.querySelectorAll(".myClass")

Option: document.getElementByClassName("myClass")

Option: document.find(".myClass")

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8. What are the benefits of using TypeScript, a superset of JavaScript, in large-scale projects?

Option: TypeScript adds optional static typing for improved code readability, maintainability, and early error detection.

Option: TypeScript requires a complete rewrite of existing JavaScript code.

Option: Not necessary for projects with good coding practices.

Option: Primarily used for server-side JavaScript with Node.js.

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9. How do you clone a JavaScript object to avoid modifying the original?

Option: Directly assigning the object to a new variable creates a clone (This is shallow copy).

Option: var newObject = Object.assign({}, oldObject);

Option: var newObject = copy(oldObject);

Option: None of the above

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10. What is the output of the following code: console.log(10 + "20");

Option: 1020

Option: 30

Option: Error

Option: 10

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11. Explain the concept of code splitting in modern JavaScript frameworks and its advantages.

Option: A technique to load different parts of the application code on demand, reducing initial bundle size and improving perceived performance.

Option: Code splitting increases the complexity of managing application state.

Option: Not recommended for production builds.

Option: Only applicable for server-side rendered applications.

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12. How do you check if a variable is an array in JavaScript?

Option: if (typeof variable === "array") { ... }

Option: if (variable instanceof Array) { ... }

Option: if (Array.isArray(variable)) { ... } (Also valid)

Option: None of the above

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13. What method is used to sort an array in JavaScript?

Option: sortNumber(array)

Option: sort(array)

Option: arrange(array)

Option: order(array)

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14. How do you define a regular expression in JavaScript?

Option: var regex = /pattern/flags;

Option: defineRegex(pattern, flags);

Option: createRegExp(pattern, flags);

Option: Regular expressions are not supported in JavaScript.

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15. How do you write a single-line comment in JavaScript?

Option: // This is a comment

Option: /* This is a comment */

Option: # This is a comment

Option: None of the above

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16. What is the scope of a variable declared with let?

Option: Global scope

Option: Block scope

Option: Function scope

Option: All of the above

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17. What are the common methods used to handle errors in asynchronous code with promises?

Option: try...catch block can be used within a promise's then or catch methods.

Option: Error handling is done manually by checking return values.

Option: JavaScript doesn't have built-in error handling for asynchronous code.

Option: All errors are automatically logged to the console.

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18. What is the purpose of a virtual DOM in libraries like React and how does it improve performance?

Option: A virtual representation of the real DOM that allows for efficient updates by identifying minimal changes before applying them to the real DOM.

Option: The virtual DOM is a separate in-memory database for storing application data.

Option: Not relevant for client-side JavaScript frameworks.

Option: Increases initial page load time.

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19. What is the correct way to define a default parameter value in a function?

Option: function name(param = value) { ... }

Option: function name(value = param) { ... }

Option: function name(param := value) { ... }

Option: None of the above

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20. Explain the concept of web workers in JavaScript and how they can be used for background tasks.

Option: Web workers are separate threads that can run long-running tasks without blocking the main thread, improving responsiveness.

Option: Web workers are not suitable for complex calculations.

Option: Communication between the main thread and web workers is limited.

Option: Web workers are a security risk and should be avoided.

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FAQ: Free JavaScript Skill Exam Certification

1. What is a JavaScript certification?

A JavaScript certification is a formal acknowledgment of your proficiency in JavaScript, demonstrating that you have the skills and knowledge to develop applications using this programming language.

2. How can I get a JavaScript certification from Microsoft and Google?

3. How do I prepare for a JavaScript certification exam?

To prepare for a JavaScript certification exam, you should: a. Study regularly using online resources and textbooks. b. Practice coding through exercises and real-world projects. c. Participate in coding bootcamps or online courses. d. Engage with study groups or online forums for support and collaboration.

4. What are the benefits of getting a JavaScript certification?

A JavaScript certification can: a. Validate your coding skills and knowledge. b. Enhance your resume and increase job opportunities. c. Potentially lead to higher salaries and career advancement. d. Provide a structured learning path and ensure you meet industry standards.

5. Can I take the JavaScript certification exam online?

Yes, most JavaScript certification exams can be taken online. Platforms like freeCodeCamp, Coursera, and Udemy offer online exams that you can complete from the comfort of your home.

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JavaScript certification course

FAQ: Free JavaScript Skill Exam Certification

1. What is a JavaScript certification?

2. How can I get a JavaScript certification from Microsoft and Google?

3. How do I prepare for a JavaScript certification exam?

4. What are the benefits of getting a JavaScript certification?

5. Can I take the JavaScript certification exam online?

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