Javascript - Variables

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1. How do you declare a variable in JavaScript using the "var" keyword?

variable myVar;

var myVar;

let myVar;

const myVar;

Difficulty

2800

medium

2. What is the difference between "let" and "var" when declaring variables in JavaScript?

"var" has block scope, while "let" has function scope.

"let" has block scope, while "var" has function scope.

Both "let" and "var" have block scope.

"var" has global scope, while "let" has block scope.

Difficulty

3600

high

3. How do you check if a variable is undefined in JavaScript?

if (myVar === undefined)

if (myVar == null)

if (typeof myVar === "undefined")

if (isUndefined(myVar))

Difficulty

2700

medium

4. What is the purpose of the "null" value in JavaScript?

It represents an empty string.

It signifies the absence of a value or a variable that has been intentionally set to no value.

It is the same as the "undefined" value.

It is a placeholder for a future value.

Difficulty

2800

medium

5. How do you concatenate strings in JavaScript using variables?

"Hello".concat(worldVar);

"Hello" + worldVar;

concat("Hello", worldVar);

join("Hello", worldVar);

Difficulty

2800

medium

6. What is the purpose of the "delete" operator in JavaScript when applied to an object property?

It removes the entire object.

It removes a specific property from an object.

It deletes the object from memory.

It deletes a variable.

Difficulty

2300

medium

7. What is the primary difference between "let" and "const" when declaring variables in JavaScript?

"let" allows reassignment, while "const" does not.

"const" allows reassignment, while "let" does not.

Both "let" and "const" allow reassignment.

Neither "let" nor "const" allows reassignment.

Difficulty

3000

medium

8. How do you declare a global variable in JavaScript?

global myVar = value;

let myVar = value;

var myVar = value;

const myVar = value;

Difficulty

2700

medium

9. What happens if you try to access an undeclared variable in JavaScript?

It returns "null."

It throws an error.

It returns "undefined."

It creates a new variable.

Difficulty

3000

medium

10. How do you concatenate a string and a variable in JavaScript?

"Hello".concat(myVar);

"Hello" + myVar;

concat("Hello", myVar);

join("Hello", myVar);

Difficulty

2800

medium

11. What is the purpose of the "delete" operator when applied to a variable in JavaScript?

It removes the variable from the memory.

It clears the variable's value.

It deletes the variable declaration.

It is not applicable to variables.

Difficulty

3000

medium

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

if (myVar === undefined)

if (myVar == null)

if (typeof myVar === "undefined")

if (isUndefined(myVar))

Difficulty

3000

medium

13. What is the purpose of the "void" operator in JavaScript when applied to a variable?

It sets the variable to null.

It converts the variable to a string.

It makes the variable undefined.

It has no effect on variables.

Difficulty

3000

medium

14. How do you swap the values of two variables in JavaScript without using a temporary variable?

[a, b] = [b, a];

a = b; b = a;

a = a + b; b = a - b; a = a - b;

swap(a, b);

Difficulty

3000

medium

15. What does the "++" operator do when applied to a variable in JavaScript?

It increments the variable after its current value is used.

It increments the variable before its current value is used.

It decreases the variable after its current value is used.

It has no effect on the variable.

Difficulty

2800

medium

16. How do you declare a variable with block scope in JavaScript?

var myVar = value;

let myVar = value;

const myVar = value;

block myVar = value;

Difficulty

3000

medium

17. What is the purpose of the "hoisting" concept in JavaScript variables?

It refers to the process of moving variable declarations to the top of their containing scope.

It involves creating variables with a higher priority in memory.

It is a way to prevent variables from being overwritten.

It is an obsolete feature in modern JavaScript.

Difficulty

2800

medium

18. How can you convert a variable to a boolean value in JavaScript?

bool(myVar)

myVar.toBoolean()

!!myVar

convertToBoolean(myVar)

Difficulty

3400

high

19. In JavaScript, what is the purpose of the "this" keyword within a function?

It refers to the global object.

It refers to the function itself.

It refers to the object that is currently executing the function.

It is not allowed within a function.

Difficulty

3600

high

20. How do you declare a variable in JavaScript without the possibility of reassignment?

let myVar = value;

const myVar = value;

var myVar = value;

declare constant myVar = value;

Difficulty

3600

high

21. How do you check if a variable is an object in JavaScript?

if (isObject(myVar))

if (myVar.type === "object")

if (typeof myVar === "object")

if (myVar.isObject())

Difficulty

3200

high

22. How can you check if a variable is an array in JavaScript?

if (isArray(myVar))

if (myVar.isArray())

if (myVar.type === "array")

if (Array.isArray(myVar))

Difficulty

3600

high

23. How do you declare a variable in JavaScript that is not bound to any specific data type?

dynamic myVar = value;

var myVar = value;

let myVar = value;

untyped myVar = value;

Difficulty

2800

medium

24. What is the purpose of the "global" object in JavaScript?

It contains all global variables and functions.

It restricts the scope of variables to the current function.

It is used for local storage operations.

It manages the execution of asynchronous functions.

Difficulty

3700

high

25. Which of the following variables takes precedence over the others if the names are the same?

Global variable

Local variable

The two of the above

None of the above

Difficulty

2500

medium

Ehsan Arvacheh

1026 points

Ovi Baidya

1019 points

Variables

Want to challenge your knowledge?

Question Bank

1. How do you declare a variable in JavaScript using the "var" keyword?

2. What is the difference between "let" and "var" when declaring variables in JavaScript?

3. How do you check if a variable is undefined in JavaScript?

4. What is the purpose of the "null" value in JavaScript?

5. How do you concatenate strings in JavaScript using variables?

6. What is the purpose of the "delete" operator in JavaScript when applied to an object property?

7. What is the primary difference between "let" and "const" when declaring variables in JavaScript?

8. How do you declare a global variable in JavaScript?

9. What happens if you try to access an undeclared variable in JavaScript?

10. How do you concatenate a string and a variable in JavaScript?

11. What is the purpose of the "delete" operator when applied to a variable in JavaScript?

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

13. What is the purpose of the "void" operator in JavaScript when applied to a variable?

14. How do you swap the values of two variables in JavaScript without using a temporary variable?

15. What does the "++" operator do when applied to a variable in JavaScript?

16. How do you declare a variable with block scope in JavaScript?

17. What is the purpose of the "hoisting" concept in JavaScript variables?

18. How can you convert a variable to a boolean value in JavaScript?

19. In JavaScript, what is the purpose of the "this" keyword within a function?

20. How do you declare a variable in JavaScript without the possibility of reassignment?

21. How do you check if a variable is an object in JavaScript?

22. How can you check if a variable is an array in JavaScript?

23. How do you declare a variable in JavaScript that is not bound to any specific data type?

24. What is the purpose of the "global" object in JavaScript?

25. Which of the following variables takes precedence over the others if the names are the same?

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