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JavaScript Data Types and Conversions Quiz

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Question 1/15

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

Number('123abc')

Select your answer

123abc

123

NaN

Question 2/15

How can you express the floating-point number 12.5 using scientific notation in JavaScript?

Select your answer

0.125e2

12.5e0

1.25e1

125e-1

Question 3/15

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

a.push(b)

append(a, b)

a.concat(' ', b)

join(a, b)

Question 4/15

Which value is obtained from the expression `"5" * "2"`?

"5" * "2"

Select your answer

NaN

"52"

Question 5/15

What does the `===` operator compare?

Select your answer

Value only

Value and type

Type only

Nothing, it's not a valid operator

Question 6/15

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

let obj = {};

Select your answer

Object.assign(obj)

new Array(obj)

Array.from(obj)

String.from(obj)

Question 7/15

What is `['a', 'b', 'c'].length` in JavaScript?

let arr = ['a', 'b', 'c'];
arr.length

Select your answer

undefined

Question 8/15

What does the `typeof` operator return for an array in JavaScript?

let arr = [1, 2, 3];
typeof arr

Select your answer

"object"

"function"

"array"

"number"

Question 9/15

What will the expression `!!"text"` evaluate to in JavaScript?

!!"text"

Select your answer

true

false

"text"

null

Question 10/15

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

Select your answer

Object

Array

Undefined

Function

Question 11/15

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

parseFloat("12.34abc")

Select your answer

"12.34abc"

NaN

12.34

Question 12/15

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

"5" - 1

Select your answer

TypeError

"51"

NaN

Question 13/15

What will `Boolean(" ")` return?

Boolean(" ")

Select your answer

TypeError

false

true

Question 14/15

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

"5" + 1

Select your answer

TypeError

"51"

NaN

Question 15/15

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

Number(undefined)

Select your answer

undefined

NaN

Your Results

You did not answer any questions correctly.

Your Answers

Question 1/15

😊 Your answer was correct 🙁 Your answer was incorrect

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

Number('123abc')

Available answers

123abc

123

NaN

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 2/15

😊 Your answer was correct 🙁 Your answer was incorrect

How can you express the floating-point number 12.5 using scientific notation in JavaScript?

Available answers

0.125e2

12.5e0

1.25e1

125e-1

In JavaScript, `1.25e1` is equal to `12.5`, where `e1` represents 10 to the power of 1.

Question 3/15

😊 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

a.push(b)

append(a, b)

a.concat(' ', b)

join(a, b)

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

Question 4/15

😊 Your answer was correct 🙁 Your answer was incorrect

Which value is obtained from the expression `"5" * "2"`?

"5" * "2"

Available answers

NaN

"52"

The `*` operator converts both strings to numbers in this case, so `"5" * "2"` equals `10`.

Question 5/15

😊 Your answer was correct 🙁 Your answer was incorrect

What does the `===` operator compare?

Available answers

Value only

Value and type

Type only

Nothing, it's not a valid operator

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

Question 6/15

😊 Your answer was correct 🙁 Your answer was incorrect

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

let obj = {};

Available answers

Object.assign(obj)

new Array(obj)

Array.from(obj)

String.from(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 7/15

😊 Your answer was correct 🙁 Your answer was incorrect

What is `['a', 'b', 'c'].length` in JavaScript?

let arr = ['a', 'b', 'c'];
arr.length

Available answers

undefined

The length property of an array returns the number of elements in the array. `['a', 'b', 'c'].length` is `3`.

Question 8/15

😊 Your answer was correct 🙁 Your answer was incorrect

What does the `typeof` operator return for an array in JavaScript?

let arr = [1, 2, 3];
typeof arr

Available answers

"object"

"function"

"array"

"number"

In JavaScript, arrays are a type of object. Therefore, `typeof` always returns `"object"` for arrays.

Question 9/15

😊 Your answer was correct 🙁 Your answer was incorrect

What will the expression `!!"text"` evaluate to in JavaScript?

!!"text"

Available answers

true

false

"text"

null

The double negation `!!` is used to convert any value to a boolean. Here, `"text"` is truthy, so `!!"text"` evaluates to `true`.

Question 10/15

😊 Your answer was correct 🙁 Your answer was incorrect

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

Available answers

Object

Array

Undefined

Function

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

Question 11/15

😊 Your answer was correct 🙁 Your answer was incorrect

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

parseFloat("12.34abc")

Available answers

"12.34abc"

NaN

12.34

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 12/15

😊 Your answer was correct 🙁 Your answer was incorrect

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

"5" - 1

Available answers

TypeError

"51"

NaN

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

Question 13/15

😊 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 14/15

😊 Your answer was correct 🙁 Your answer was incorrect

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

"5" + 1

Available answers

TypeError

"51"

NaN

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 15/15

😊 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`.