Basic JavaScript Interview question and answers


Q1. What is JavaScript?
A1. JavaScript is a scripting language used to create and control dynamic website content, 
such as forms, animations, and interactive elements.

Q2. What are the data types in JavaScript?
A2. The data types in JavaScript include: strings, numbers, booleans, 
objects, arrays, and functions.

Q3. How do you define a variable in JavaScript?
A3. Variables can be defined in JavaScript using the “var” keyword 
followed by the variable name.

Q4. What is the purpose of the “this” keyword in JavaScript?
A4. The “this” keyword is used to refer to the object that the current 
code is being executed in.

Q5. What is the difference between == and === in JavaScript?
A5. The “==” operator checks if two values are equal in value, while the “===” 
operator checks if two values are equal in value and type.

Q6. What is the purpose of the “undefined” keyword in JavaScript?
A6. The “undefined” keyword is used to denote a variable that has been declared, 
but not yet assigned a value.

Q7. What is the purpose of the “null” keyword in JavaScript?
A7. The “null” keyword is used to denote an empty value.

Q8. What is the purpose of a function in JavaScript?
A8. Functions are used to encapsulate code that can be reused throughout a program.

Q9. How do you define a function in JavaScript?
A9. Functions are defined using the “function” keyword followed by the function name, 
parameters, and code block.

Q10. What is the purpose of an array in JavaScript?
A10. Arrays are used to store multiple values in a single variable.

Q11. How do you create an array in JavaScript?
A11. Arrays are created using the “new Array()” constructor, or by using the square 
bracket notation.

Q12. What is the purpose of an object in JavaScript?
A12. Objects are used to store and organize data in a structured way.

Q13. How do you create an object in JavaScript?
A13. Objects are created using the “new Object()” constructor, or by using the object 
literal notation.

Q14. What is the purpose of a loop in JavaScript?
A14. Loops are used to repeat a set of instructions until a certain condition is met.

Q15. How do you create a loop in JavaScript?
A15. Loops are created using the “for”, “while”, or “do-while” statements.

Q16. What is the purpose of an if statement in JavaScript?
A16. If statements are used to execute code based on a certain condition.

Q17. How do you create an if statement in JavaScript?
A17. If statements are created using the “if” keyword followed by a condition.

Q18. What is the purpose of an event handler in JavaScript?
A18. Event handlers are used to execute code when a certain event occurs.

Q19. How do you create an event handler in JavaScript?
A19. Event handlers are created using the “on” keyword followed by the event name and 
code block.

Q20. What is the purpose of a try/catch block in JavaScript?
A20. Try/catch blocks are used to handle errors that occur in a program.

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