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JavaScript Data Types and Conversions Quiz

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Question 1/15

What does `parseFloat("12.34abc")` return in JavaScript?

parseFloat("12.34abc")

Select your answer

12.34

NaN

"12.34abc"

Question 2/15

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

Number(undefined)

Select your answer

NaN

undefined

Question 3/15

How do you convert a string `"123"` to a number in JavaScript?

Select your answer

"123".parseNumber()

Number("123")

parseFloat(123)

parseInt(123.45)

Question 4/15

What result will `typeof undefined` produce?

typeof undefined

Select your answer

"undefined"

"null"

"string"

"object"

Question 5/15

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

parseInt("10.5")

Select your answer

"10.5"

10.5

NaN

Question 6/15

What is the result of the expression `typeof null` in JavaScript?

typeof null

Select your answer

"string"

"object"

"undefined"

"null"

Question 7/15

What will `Boolean(" ")` return?

Boolean(" ")

Select your answer

TypeError

false

true

Question 8/15

What is the result of `"5" - 1` in JavaScript?

"5" - 1

Select your answer

NaN

TypeError

"51"

Question 9/15

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

Select your answer

do...while loop

while loop

for...in loop

for loop

Question 10/15

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

Select your answer

String

Array

Object

Date

Question 11/15

What is the value of `Number('123abc')` in JavaScript?

Number('123abc')

Select your answer

123abc

NaN

123

Question 12/15

Which statement will create an object from an empty object in JavaScript?

let obj = {};

Select your answer

Array.from(obj)

new Array(obj)

String.from(obj)

Object.assign(obj)

Question 13/15

Which JavaScript type has no methods or properties of its own?

Select your answer

Array

Function

Object

Undefined

Question 14/15

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

append(a, b)

a.concat(' ', b)

join(a, b)

a.push(b)

Question 15/15

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

Boolean("false")

Select your answer

false

true

TypeError

null

Your Results

You did not answer any questions correctly.

Your Answers

Question 1/15

😊 Your answer was correct 🙁 Your answer was incorrect

What does `parseFloat("12.34abc")` return in JavaScript?

parseFloat("12.34abc")

Available answers

12.34

NaN

"12.34abc"

The `parseFloat` function converts a string to a floating-point number up to the first invalid character. Thus, `parseFloat("12.34abc")` returns `12.34`.

Question 2/15

😊 Your answer was correct 🙁 Your answer was incorrect

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

Number(undefined)

Available answers

NaN

undefined

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 3/15

😊 Your answer was correct 🙁 Your answer was incorrect

How do you convert a string `"123"` to a number in JavaScript?

Available answers

"123".parseNumber()

Number("123")

parseFloat(123)

parseInt(123.45)

You can convert a string to a number using the `Number` function, like so: `Number("123")`.

Question 4/15

😊 Your answer was correct 🙁 Your answer was incorrect

What result will `typeof undefined` produce?

typeof undefined

Available answers

"undefined"

"null"

"string"

"object"

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

Question 5/15

😊 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 6/15

😊 Your answer was correct 🙁 Your answer was incorrect

What is the result of the expression `typeof null` in JavaScript?

typeof null

Available answers

"string"

"object"

"undefined"

"null"

In JavaScript, `typeof null` returns `"object"`. This is a well-known bug in JavaScript introduced in the first version of the language.

Question 7/15

😊 Your answer was correct 🙁 Your answer was incorrect

What will `Boolean(" ")` return?

Boolean(" ")

Available answers

TypeError

false

true

The `Boolean` conversion of any non-empty string will return `true`, including a space character.

Question 8/15

😊 Your answer was correct 🙁 Your answer was incorrect

What is the result of `"5" - 1` in JavaScript?

"5" - 1

Available answers

NaN

TypeError

"51"

In JavaScript, the `-` operator converts operands to numbers if they're not, so `"5" - 1` evaluates to `4`.

Question 9/15

😊 Your answer was correct 🙁 Your answer was incorrect

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

Available answers

do...while loop

while loop

for...in loop

for loop

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

Question 10/15

😊 Your answer was correct 🙁 Your answer was incorrect

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

Available answers

String

Array

Object

Date

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

Question 11/15

😊 Your answer was correct 🙁 Your answer was incorrect

What is the value of `Number('123abc')` in JavaScript?

Number('123abc')

Available answers

123abc

NaN

123

The `Number` function returns `NaN` when a string cannot be converted to a number. Since `'123abc'` is not a valid number, the result is `NaN`.

Question 12/15

😊 Your answer was correct 🙁 Your answer was incorrect

Which statement will create an object from an empty object in JavaScript?

let obj = {};

Available answers

Array.from(obj)

new Array(obj)

String.from(obj)

Object.assign(obj)

`Object.assign` can be used to copy all enumerable properties from one (or more) source objects to a target object. `Object.assign(obj)` will just return `obj` if it doesn't have another source object.

Question 13/15

😊 Your answer was correct 🙁 Your answer was incorrect

Which JavaScript type has no methods or properties of its own?

Available answers

Array

Function

Object

Undefined

`Undefined` is a primitive data type in JavaScript, which has no properties or methods.

Question 14/15

😊 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

append(a, b)

a.concat(' ', b)

join(a, b)

a.push(b)

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

Question 15/15

😊 Your answer was correct 🙁 Your answer was incorrect

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

Boolean("false")

Available answers

false

true

TypeError

null

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.