JavaScript Data Types and Conversions Quiz

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Question 1/15

What is `typeof NaN` in JavaScript? 
typeof NaN

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Question 2/15

What is `['a', 'b', 'c'].length` in JavaScript? 
let arr = ['a', 'b', 'c'];
arr.length

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Question 3/15

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

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Question 4/15

What result will `typeof undefined` produce? 
typeof undefined

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Question 5/15

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

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Question 6/15

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

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Question 7/15

What does the `===` operator compare?

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Question 8/15

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

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Question 9/15

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

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Question 10/15

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

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Question 11/15

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

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Question 12/15

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

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Question 13/15

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

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Question 14/15

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

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Question 15/15

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

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Your Answers

Question 1/15
😊 Your answer was correct 🙁 Your answer was incorrect
What is `typeof NaN` in JavaScript? 
typeof NaN

Available answers

Despite being "Not-a-Number", `NaN` is of type `number` in JavaScript.
Question 2/15
😊 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

The length property of an array returns the number of elements in the array. `['a', 'b', 'c'].length` is `3`.
Question 3/15
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How do you correctly check if a variable is a string in JavaScript?

Available answers

Use `typeof variable === 'string'` to check if a variable is of type string properly.
Question 4/15
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What result will `typeof undefined` produce? 
typeof undefined

Available answers

In JavaScript, the `typeof` operator used on `undefined` returns `"undefined"`.
Question 5/15
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What will the expression `!!"text"` evaluate to in JavaScript? 
!!"text"

Available answers

The double negation `!!` is used to convert any value to a boolean. Here, `"text"` is truthy, so `!!"text"` evaluates to `true`.
Question 6/15
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Which of the following is a primitive data type in JavaScript?

Available answers

Strings, numbers, booleans, null, and undefined are the primitive data types in JavaScript. `String` is one of them.
Question 7/15
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What does the `===` operator compare?

Available answers

The `===` operator in JavaScript checks for both value and type equality.
Question 8/15
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How can you express the floating-point number 12.5 using scientific notation in JavaScript?

Available answers

In JavaScript, `1.25e1` is equal to `12.5`, where `e1` represents 10 to the power of 1.
Question 9/15
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What value is returned by the expression `Number(undefined)` in JavaScript? 
Number(undefined)

Available answers

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 10/15
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What does `parseFloat("12.34abc")` return in JavaScript? 
parseFloat("12.34abc")

Available answers

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 11/15
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If `let x;`, what is `x` initialized to? 
let x;

Available answers

Variables declared using `let` without an initializer are initialized to `undefined`.
Question 12/15
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How can you check if a number is not a number using a built-in JavaScript function?

Available answers

The `isNaN` function checks whether a value is `NaN`. If the result of the expression is `NaN`, `isNaN` returns `true`.
Question 13/15
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Which value is obtained from the expression `"5" * "2"`? 
"5" * "2"

Available answers

The `*` operator converts both strings to numbers in this case, so `"5" * "2"` equals `10`.
Question 14/15
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How do you convert a string `"123"` to a number in JavaScript?

Available answers

You can convert a string to a number using the `Number` function, like so: `Number("123")`.
Question 15/15
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What is the value of `Boolean("false")` in JavaScript? 
Boolean("false")

Available answers

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.