Which keyword is used to declare a block-scoped variable that can be reassigned?
1. Which keyword is used to declare a block-scoped variable that can be reassigned?
- A.var
- B.const
- C.let
- D.define
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JavaScript - Basics
Array methods, object property access, type coercion, and NaN checking.
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Which keyword is used to declare a block-scoped variable that cannot be reassigned (read-only)?
2. Which keyword is used to declare a block-scoped variable that cannot be reassigned (read-only)?
- A.let
- B.var
- C.const
- D.immutable
Which logical operator represents logical NOT?
3. Which logical operator represents logical NOT?
- A.not
- B.&&
- C.!
- D.||
Which logical operator represents logical OR?
4. Which logical operator represents logical OR?
- A.&&
- B.!
- C.||
- D.|
Which operator is the modulus operator used to get the remainder of a division?
5. Which operator is the modulus operator used to get the remainder of a division?
- A./
- B.mod
- C.%
- D.div
What is the return type of the expression `typeof NaN`?
6. What is the return type of the expression `typeof NaN`?
- A.NaN
- B.undefined
- C.number
- D.object
Which operator is the strict equality operator that compares both value and type?
7. Which operator is the strict equality operator that compares both value and type?
- A.==
- B.=
- C.===
- D.equal
What does the `typeof` operator return for `null` in JavaScript?
8. What does the `typeof` operator return for `null` in JavaScript?
- A.null
- B.undefined
- C.object
- D.value
What does `NaN` stand for in JavaScript?
9. What does `NaN` stand for in JavaScript?
- A.Null and Nullify
- B.New Array Number
- C.Not-a-Number
- D.Negative Auxiliary Number
What does the `typeof` operator return for an undefined variable?
10. What does the `typeof` operator return for an undefined variable?
- A.null
- B.object
- C.undefined
- D.error
What is the scope of a variable declared with the `var` keyword?
11. What is the scope of a variable declared with the `var` keyword?
- A.Block scope
- B.Local scope only to curly braces
- C.Function scope
- D.No scope restrictions
What is the difference between `==` and `===` operators?
12. What is the difference between `==` and `===` operators?
- A.=== performs type coercion; == does not.
- B.== is for strings; === is for numbers.
- C.== performs type coercion; === does not.
- D.There is no difference; they are identical.
Which logical operator represents logical AND?
13. Which logical operator represents logical AND?
- A.||
- B.!
- C.&&
- D.&
How do you write a single-line comment in JavaScript?
14. How do you write a single-line comment in JavaScript?
- A./* this is a comment */
- B.# this is a comment
- C.// this is a comment
- D.<!-- this is a comment -->
Which built-in function displays a dialog box with a message and an OK button to alert users?
15. Which built-in function displays a dialog box with a message and an OK button to alert users?
- A.console.log()
- B.prompt()
- C.alert()
- D.confirm()
Which built-in method writes messages to the developer console for debugging?
16. Which built-in method writes messages to the developer console for debugging?
- A.print()
- B.document.write()
- C.console.log()
- D.alert()
Which built-in function prompts the user to enter text input in a dialog box?
17. Which built-in function prompts the user to enter text input in a dialog box?
- A.alert()
- B.confirm()
- C.prompt()
- D.input()
How do you write a multi-line comment in JavaScript?
18. How do you write a multi-line comment in JavaScript?
- A.// this is a comment
- B.<!-- this is a comment -->
- C./* this is a comment */
- D.## this is a comment ##
How do you create a basic empty object in JavaScript?
19. How do you create a basic empty object in JavaScript?
- A.let person = [];
- B.let person = ();
- C.let person = {};
- D.let person = Object.empty();
What index represents the first element in a JavaScript array?
20. What index represents the first element in a JavaScript array?
- A.1
- B.-1
- C.0
- D.0.1
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