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JavaScript Data Types and Conversions Quiz

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Question 1/15

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

let obj = {};

Select your answer

Array.from(obj)

String.from(obj)

new Array(obj)

Object.assign(obj)

Question 2/15

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)

join(a, b)

a.concat(' ', b)

Question 3/15

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

parseFloat("12.34abc")

Select your answer

12.34

NaN

"12.34abc"

Question 4/15

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

b === c

b == c

a === b

a == b

Question 5/15

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

Boolean("false")

Select your answer

null

TypeError

false

true

Question 6/15

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

Select your answer

String(variable)

typeof variable == String

typeof variable === 'string'

variable == String

Question 7/15

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

Select your answer

Function

Undefined

Array

Object

Question 8/15

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

Number(undefined)

Select your answer

undefined

NaN

Question 9/15

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

let x;

Select your answer

x === undefined

x != null

x == "undefined"

typeof x === 'undefined'

Question 10/15

What does the `===` operator compare?

Select your answer

Value only

Value and type

Type only

Nothing, it's not a valid operator

Question 11/15

How can you check if a number is not a number using a built-in JavaScript function?

Select your answer

isNaN(value)

typeof value === "NaN"

isNotNumber(value)

checkNaN(value)

Question 12/15

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

"5" - 1

Select your answer

TypeError

NaN

"51"

Question 13/15

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

Select your answer

Object

Date

Array

String

Question 14/15

Which of the following is NOT a falsy value in JavaScript?

Select your answer

NaN

undefined

"false"

Question 15/15

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

"5" * "2"

Select your answer

NaN

"52"

Your Results

You did not answer any questions correctly.

Your Answers

Question 1/15

😊 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)

String.from(obj)

new Array(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 2/15

😊 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)

join(a, b)

a.concat(' ', b)

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

Question 3/15

😊 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 4/15

😊 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

b === c

b == c

a === b

a == b

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 5/15

😊 Your answer was correct 🙁 Your answer was incorrect

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

Boolean("false")

Available answers

null

TypeError

false

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 6/15

😊 Your answer was correct 🙁 Your answer was incorrect

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

Available answers

String(variable)

typeof variable == String

typeof variable === 'string'

variable == String

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

Question 7/15

😊 Your answer was correct 🙁 Your answer was incorrect

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

Available answers

Function

Undefined

Array

Object

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

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

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

let x;

Available answers

x === undefined

x != null

x == "undefined"

typeof 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 10/15

😊 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 11/15

😊 Your answer was correct 🙁 Your answer was incorrect

How can you check if a number is not a number using a built-in JavaScript function?

Available answers

isNaN(value)

typeof value === "NaN"

isNotNumber(value)

checkNaN(value)

The `isNaN` function checks whether a value is `NaN`. If the result of the expression is `NaN`, `isNaN` returns `true`.

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

NaN

"51"

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

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 14/15

😊 Your answer was correct 🙁 Your answer was incorrect

Which of the following is NOT a falsy value in JavaScript?

Available answers

NaN

undefined

"false"

In JavaScript, the string "false" is not falsy. Falsy values include `false`, `0`, `NaN`, `""` (empty string), `null`, and `undefined`.

Question 15/15

😊 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`.