Part 8–100 Advanced JavaScript Interview Questions with Answers and Code Examples

Welcome to the eighth part of our series on advanced JavaScript interview questions!

Introduction:

In this article, we’ll continue our exploration of ten more challenging questions that will test your knowledge of JavaScript concepts and techniques. Each question is accompanied by a detailed answer and code examples to help you understand the topic thoroughly. Additionally, we’ll provide external links for further reading to enhance your understanding. Let’s jump right in!

71- What is the purpose of the “Object.entries()” method in JavaScript? Provide an example.

Answer: The Object.entries() method returns an array of a given object's own enumerable string-keyed property [key, value] pairs. Here's an example:

const person = {
  name: 'John',
  age: 30,
  city: 'New York'
};
const entries = Object.entries(person);
console.log(entries);
// Output: [['name', 'John'], ['age', 30], ['city', 'New York']]

Further Reading: MDN Web Docs — Object.entries()

72- How can you copy an object in JavaScript? Provide an example.

Answer: To copy an object in JavaScript, you can use various techniques such as the spread operator ({...}), Object.assign(), or the JSON.parse() and JSON.stringify() combination. Here's an example using the spread operator:

const original = { name: 'John', age: 30 };
const copy = { ...original };
console.log(copy);
// Output: { name: 'John', age: 30 }

External link: MDN Web Docs — Spread syntax

73- What is the purpose of the “Set” data structure in JavaScript? Provide an example.

Answer: The Set data structure in JavaScript is an ordered collection of unique values, where duplicates are not allowed. Here's an example:

const set = new Set();
set.add(1);
set.add(2);
set.add(3);
console.log(set); // Output: Set { 1, 2, 3 }

Further Reading: MDN Web Docs — Set

74- How can you check if a value is NaN (Not a Number) in JavaScript? Provide an example.

Answer: To check if a value is NaN in JavaScript, you can use the isNaN() function or the Number.isNaN() method. Here's an example using Number.isNaN():

console.log(Number.isNaN('Hello')); // Output: false
console.log(Number.isNaN(42)); // Output: false
console.log(Number.isNaN(NaN)); // Output: true

Further Reading: MDN Web Docs — Number.isNaN()

75- What is the purpose of the “String.fromCharCode()” method in JavaScript? Provide an example.

Answer: The String.fromCharCode() method returns a string created from the specified sequence of Unicode values. Here's an example:

const charCode = 65;
console.log(String.fromCharCode(charCode)); // Output: A

Further Reading: MDN Web Docs — String.fromCharCode()

76- How can you merge two arrays in JavaScript? Provide an example.

Answer: To merge two arrays in JavaScript, you can use various methods such as the spread operator ([...]), concat(), or the push() method. Here's an example using the spread operator:

const array1 = [1, 2, 3];
const array2 = [4, 5, 6];
const mergedArray = [...array1, ...array2];
console.log(mergedArray);
// Output: [1, 2, 3, 4, 5, 6]

Further Reading: MDN Web Docs — Spread syntax

77- What is the purpose of the “Math.random()” method in JavaScript? Provide an example.

Answer: The Math.random() method returns a random floating-point number between 0 and 1 (inclusive of 0, but not 1). Here's an example:

const randomNumber = Math.random();
console.log(randomNumber); // Output: a random number between 0 and 1

Further Reading: MDN Web Docs — Math.random()

78- How can you convert a string to uppercase or lowercase in JavaScript? Provide an example.

Answer: To convert a string to uppercase or lowercase in JavaScript, you can use the toUpperCase() and toLowerCase() methods, respectively. Here's an example:

const str = 'Hello, World!';
console.log(str.toUpperCase()); // Output: HELLO, WORLD!
console.log(str.toLowerCase()); // Output: hello, world!

Further Reading:

• MDN Web Docs — String.prototype.toUpperCase()
• MDN Web Docs — String.prototype.toLowerCase()

79- What is the purpose of the “Array.isArray()” method in JavaScript? Provide an example.

Answer: The Array.isArray() method determines whether a value is an array. Here's an example:

console.log(Array.isArray([1, 2, 3])); // Output: true
console.log(Array.isArray('Hello')); // Output: false

Further Reading: MDN Web Docs — Array.isArray()

80- How can you remove the first element from an array in JavaScript? Provide an example.

Answer: To remove the first element from an array in JavaScript, you can use the shift() method. Here's an example:

const array = [1, 2, 3];
array.shift();
console.log(array); // Output: [2, 3]

Further Reading: MDN Web Docs — Array.prototype.shift()

That concludes the eighth part of our series on advanced JavaScript interview questions. We hope you found these questions and answers informative and helpful. In the next article, we’ll cover the final set of ten questions to further expand your JavaScript knowledge. Stay tuned!

Remember to check the provided external links for further reading to enhance your understanding of the topics.

Next Article: Part 9

Previous Articles:

Part 1–100 Advanced JavaScript Interview Questions with Answers and Code Examples

Part 2–100 Advanced JavaScript Interview Questions with Answers and Code Examples

Part 3–100 Advanced JavaScript Interview Questions with Answers and Code Examples

Part 4–100 Advanced JavaScript Interview Questions with Answers and Code Examples

Part 5–100 Advanced JavaScript Interview Questions with Answers and Code Examples

Part 6–100 Advanced JavaScript Interview Questions with Answers and Code Examples

Part 7–100 Advanced JavaScript Interview Questions with Answers and Code Examples

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