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?

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Question 2/15

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

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Question 3/15

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

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Question 4/15

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

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Question 5/15

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

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Question 6/15

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

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Question 7/15

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

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Question 8/15

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

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Question 9/15

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

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Question 10/15

What is `typeof NaN` in JavaScript?
typeof NaN

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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;

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Question 12/15

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

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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';

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Question 14/15

What result will `typeof undefined` produce?
typeof undefined

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Question 15/15

What does the `===` operator compare?

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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

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

The number `0` is a falsy value, so `Boolean(0)` evaluates to `false`.
Question 3/15
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What will `"5" + 1` evaluate to in JavaScript?
"5" + 1

Available answers

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

Available answers

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
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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 6/15
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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 7/15
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What does `parseInt("10.5")` return in JavaScript?
parseInt("10.5")

Available answers

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
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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 9/15
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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.
Question 10/15
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What is `typeof NaN` in JavaScript?
typeof NaN

Available answers

Despite being "Not-a-Number", `NaN` is of type `number` in JavaScript.
Question 11/15
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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

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
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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 13/15
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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

In JavaScript, you use `a.concat(' ', b)` to combine two strings.
Question 14/15
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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 15/15
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What does the `===` operator compare?

Available answers

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