Unit 4: JavaScript Fundamentals - Practice Quiz

1 What is JavaScript primarily used for in web development?

2 Which HTML element is used to include JavaScript code in a web page?

3 Which keyword declares a block-scoped variable that can be reassigned?

4 Which keyword declares a block-scoped binding that cannot be reassigned?

5 What is the data type of the value "JavaScript"?

6 Which JavaScript value represents an intentionally empty or absent value?

7 Which operator checks both value and data type for equality?

8 What is the result of the expression 10 % 3?

9 Which property returns the number of characters in a string named text?

10 Which method converts the string name to uppercase?

11 Which pair contains the two Boolean values in JavaScript?

12 What does Number("25") return?

13 Which statement runs a block of code only when a specified condition is true?

14 Which keyword provides an alternative block when an if condition is false?

15 Which keyword is commonly used to declare a JavaScript function?

16 Which keyword sends a value back from a function?

17 Where can a variable declared inside a function normally be accessed?

18 Which method adds an element to the end of an array?

19 Which index accesses the first element of a JavaScript array named items?

20 How can the name property of an object called student be accessed using dot notation?

21 What happens when a browser encounters <script defer src="app.js"></script> in the document <head>?

22 Given const user = { name: "Ana" };, which statement executes without causing an error?

23 What is printed by console.log(typeof null, Array.isArray([]));?

24 What is the output of console.log(0 ?? 5, 0 || 5);?

25 What value is produced by the expression 2 + 3 * 4 ** 2?

26 What does "JavaScript".slice(4, 10) return?

27 What is printed by let text = " web "; text.trim().toUpperCase(); console.log(text.length);?

28 What is printed by console.log(Number.isNaN("hello"), isNaN("hello"));?

29 What is the value of [0, 1, "", "JS", null].filter(Boolean).length?

30 What is printed by const age = 20; const hasID = false; if (age >= 18 && hasID) { console.log("Enter"); } else if (age >= 18) { console.log("ID required"); } else { console.log("Too young"); }?

31 What is printed by const value = "2"; switch (value) { case 2: console.log("number"); break; case "2": console.log("string"); break; default: console.log("other"); }?

32 What is returned by function total(price, tax = price * 0.1) { return price + tax; } total(200);?

33 What is the result of function twice(fn, value) { return fn(fn(value)); } twice(x => x + 3, 4);?

34 What is printed by let count = 10; { let count = 20; console.log(count); } console.log(count);?

35 What is returned by function makeFunctions() { const result = []; for (let i = 0; i < 3; i++) result.push(() => i); return result; } makeFunctions().map(fn => fn());?

36 After const values = [1, 2, 3, 4]; const removed = values.splice(1, 2, 9);, what are values and removed?

37 What is the result of [1, 2, 3, 4].filter(n => n % 2 === 0).map(n => n * n)?

38 What value is returned by [2, 3, 4].reduce((product, n) => product * n, 1)?

39 What is printed by const original = { info: { score: 1 } }; const copy = { ...original }; copy.info.score = 5; console.log(original.info.score);?

40 What is printed by const item = { name: "Pen", price: 10 }; const { name: label, stock = 0 } = item; console.log(label, stock);?

41 What is printed by the following JavaScript code?

console.log("A");
Promise.resolve().then(() => console.log("B"));
queueMicrotask(() => console.log("C"));
setTimeout(() => console.log("E"), 0);
console.log("D");

42 What happens when this code executes?

let x = 1;

function test() {
  console.log(x);
  let x = 2;
}

test();

43 In an ordinary non-strict script, what is printed?

const config = Object.freeze({
  nested: { value: 1 }
});

config.nested.value = 2;
config.nested = { value: 3 };
console.log(config.nested.value);

44 What is the value of result?

const value = Object.create(null);
const result = [
  typeof value,
  value instanceof Object,
  Object.getPrototypeOf(value)
];

45 What are the final values of x and y?

let x = 0;
const y = x++ || ++x;

46 What happens when an ECMAScript parser processes this statement?

const result = null ?? false || true;

47 What is the value of result?

const text = "A😀B";
const result = [
  text.length,
  text.slice(1, 3),
  Array.from(text).length
];

48 What does the following expression return?

"aba".replace(/a/g, (match, offset) => String(offset))

49 What is the result of this comparison?

Number.MAX_SAFE_INTEGER + 1 === Number.MAX_SAFE_INTEGER + 2

50 What is the value of result?

const result = [
  Object.is(NaN, NaN),
  Object.is(0, -0),
  Boolean(new Boolean(false))
];

51 What is the final value of result?

let result = "";

switch (2) {
  case 1:
    result += "A";
  case 2:
    result += "B";
  default:
    result += "C";
  case 3:
    result += "D";
}

52 What is the value of result after this code runs?

let a = 0;
let b = 1;
let result;

if (a = b && 0 || 2) {
  result = [a, "T"];
} else {
  result = [a, "F"];
}

53 What happens when f() is called?

let x = 10;

function f(a = x, x = 20) {
  return [a, x];
}

f();

54 What does the final expression return?

const obj = {
  x: 5,
  make() {
    return () => this.x;
  }
};

const fn = obj.make();
const other = { x: 9, fn };
other.fn();

55 What string is produced?

const callbacks = [];

for (var i = 0; i < 3; i++) {
  let j = i;
  callbacks.push(() => `${i}:${j}`);
}

callbacks.map(fn => fn()).join(",");

56 What is the value of result?

const source = [1, , 3];
const mapped = source.map(x => x * 2);
const result = [
  mapped.length,
  0 in mapped,
  1 in mapped,
  2 in mapped
];

57 After this code runs, what are removed and values?

const values = [1, 2, 3, 4];
const removed = values.splice(1, 2, 9, 8, 7);

58 What is the value of result?

const symbol = Symbol("1");
const object = {
  [1]: "first",
  "1": "second",
  [symbol]: "third"
};

const result = [
  Object.keys(object),
  object[1],
  Object.getOwnPropertySymbols(object).length
];

59 What is the value of result?

const source = {
  get x() {
    return 2;
  }
};

const target = { ...source };
const descriptor = Object.getOwnPropertyDescriptor(target, "x");
const result = [target.x, typeof descriptor.get, descriptor.writable];

60 What is the value of result?

const prototype = { x: 1 };
const object = Object.create(prototype);
object.x = 2;
delete object.x;

const result = [
  "x" in object,
  Object.hasOwn(object, "x"),
  object.x
];