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JavaScript Data Types and Conversions Quiz

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Question 1/15

In JavaScript, which type of loop will run at least once no matter what?

Select your answer

for...in loop

for loop

while loop

do...while loop

Question 2/15

What does the `console.log(Boolean(0))` output in JavaScript?

console.log(Boolean(0))

Select your answer

Error

false

true

Question 3/15

What will `"5" + 1` evaluate to in JavaScript?

"5" + 1

Select your answer

NaN

TypeError

"51"

Question 4/15

Which statement will determine if the variable `x` is undefined?

let x;

Select your answer

typeof x === 'undefined'

x == "undefined"

x != null

x === undefined

Question 5/15

Which of the following is a primitive data type in JavaScript?

Select your answer

Object

Date

Array

String

Question 6/15

If `let x;`, what is `x` initialized to?

let x;

Select your answer

NaN

undefined

null

Question 7/15

What does `parseInt("10.5")` return in JavaScript?

parseInt("10.5")

Select your answer

"10.5"

10.5

NaN

Question 8/15

What value is returned by the expression `Number(undefined)` in JavaScript?

Number(undefined)

Select your answer

undefined

NaN

Question 9/15

What is the value of `Boolean("false")` in JavaScript?

Boolean("false")

Select your answer

false

TypeError

null

true

Question 10/15

What is `typeof NaN` in JavaScript?

typeof NaN

Select your answer

"object"

"NaN"

"number"

"undefined"

Question 11/15

Which of the following expressions will evaluate to `true`?

let a = 0;
let b = "0";
let c = false;
// expressions
a == b;
a === b;
b == c;
b === c;

Select your answer

a == b

a === b

b === c

b == c

Question 12/15

How do you correctly check if a variable is a string in JavaScript?

Select your answer

typeof variable === 'string'

variable == String

typeof variable == String

String(variable)

Question 13/15

Which JavaScript function would you use to combine variable `let a = 'Hello'; let b = 'World';` into a single output 'Hello World'?

let a = 'Hello';
let b = 'World';

Select your answer

join(a, b)

a.concat(' ', b)

append(a, b)

a.push(b)

Question 14/15

What result will `typeof undefined` produce?

typeof undefined

Select your answer

"undefined"

"string"

"object"

"null"

Question 15/15

What does the `===` operator compare?

Select your answer

Nothing, it's not a valid operator

Value only

Value and type

Type only

Your Results

You did not answer any questions correctly.

Your Answers

Question 1/15

😊 Your answer was correct 🙁 Your answer was incorrect

In JavaScript, which type of loop will run at least once no matter what?

Available answers

for...in loop

for loop

while loop

do...while loop

A `do...while` loop will execute the block of code at least once before checking the condition.

Question 2/15

😊 Your answer was correct 🙁 Your answer was incorrect

What does the `console.log(Boolean(0))` output in JavaScript?

console.log(Boolean(0))

Available answers

Error

false

true

The number `0` is a falsy value, so `Boolean(0)` evaluates to `false`.

Question 3/15

😊 Your answer was correct 🙁 Your answer was incorrect

What will `"5" + 1` evaluate to in JavaScript?

"5" + 1

Available answers

NaN

TypeError

"51"

In JavaScript, when using the + operator with a string and a number, the number is converted to a string, and string concatenation occurs. Thus, `"5" + 1` evaluates to `"51"`.

Question 4/15

😊 Your answer was correct 🙁 Your answer was incorrect

Which statement will determine if the variable `x` is undefined?

let x;

Available answers

typeof x === 'undefined'

x == "undefined"

x != null

x === undefined

The `typeof` operator returns a string indicating the type of the unevaluated operand. To check if a variable is `undefined`, use `typeof x === 'undefined'` which safely checks even if `x` is undeclared.

Question 5/15

😊 Your answer was correct 🙁 Your answer was incorrect

Which of the following is a primitive data type in JavaScript?

Available answers

Object

Date

Array

String

Strings, numbers, booleans, null, and undefined are the primitive data types in JavaScript. `String` is one of them.

Question 6/15

😊 Your answer was correct 🙁 Your answer was incorrect

If `let x;`, what is `x` initialized to?

let x;

Available answers

NaN

undefined

null

Variables declared using `let` without an initializer are initialized to `undefined`.

Question 7/15

😊 Your answer was correct 🙁 Your answer was incorrect

What does `parseInt("10.5")` return in JavaScript?

parseInt("10.5")

Available answers

"10.5"

10.5

NaN

The `parseInt` function converts a string to an integer. It parses up to the first invalid character for an integer, so `parseInt("10.5")` returns `10`.

Question 8/15

😊 Your answer was correct 🙁 Your answer was incorrect

What value is returned by the expression `Number(undefined)` in JavaScript?

Number(undefined)

Available answers

undefined

NaN

The `Number` function converts the value to a number. If it can't be converted to a number, it will return `NaN`. `undefined` is converted to `NaN`.

Question 9/15

😊 Your answer was correct 🙁 Your answer was incorrect

What is the value of `Boolean("false")` in JavaScript?

Boolean("false")

Available answers

false

TypeError

null

true

When a string that is not empty (including the string "false") is converted to a boolean in JavaScript, it results in `true`. Non-empty strings are truthy values.

Question 10/15

😊 Your answer was correct 🙁 Your answer was incorrect

What is `typeof NaN` in JavaScript?

typeof NaN

Available answers

"object"

"NaN"

"number"

"undefined"

Despite being "Not-a-Number", `NaN` is of type `number` in JavaScript.

Question 11/15

😊 Your answer was correct 🙁 Your answer was incorrect

Which of the following expressions will evaluate to `true`?

let a = 0;
let b = "0";
let c = false;
// expressions
a == b;
a === b;
b == c;
b === c;

Available answers

a == b

a === b

b === c

b == c

The `==` operator allows type coercion and `0`, `"0"`, and `false` are loosely equal in JavaScript, so `a == b` evaluates to `true`. However, `a === b`, which checks for both value and type equality, returns `false`.

Question 12/15

😊 Your answer was correct 🙁 Your answer was incorrect

How do you correctly check if a variable is a string in JavaScript?

Available answers

typeof variable === 'string'

variable == String

typeof variable == String

String(variable)

Use `typeof variable === 'string'` to check if a variable is of type string properly.

Question 13/15

😊 Your answer was correct 🙁 Your answer was incorrect

Which JavaScript function would you use to combine variable `let a = 'Hello'; let b = 'World';` into a single output 'Hello World'?

let a = 'Hello';
let b = 'World';

Available answers

join(a, b)

a.concat(' ', b)

append(a, b)

a.push(b)

In JavaScript, you use `a.concat(' ', b)` to combine two strings.

Question 14/15

😊 Your answer was correct 🙁 Your answer was incorrect

What result will `typeof undefined` produce?

typeof undefined

Available answers

"undefined"

"string"

"object"

"null"

In JavaScript, the `typeof` operator used on `undefined` returns `"undefined"`.

Question 15/15

😊 Your answer was correct 🙁 Your answer was incorrect

What does the `===` operator compare?

Available answers

Nothing, it's not a valid operator

Value only

Value and type

Type only

The `===` operator in JavaScript checks for both value and type equality.