This content originally appeared on Level Up Coding - Medium and was authored by FardaKarimov
With the competition in the job market, it’s not surprising that the interview process can be rigorous. As a JavaScript developer, you need to have a deep understanding of the language and its quirks. However, there are certain questions that tend to stump even the most experienced developers. In this article, we will explore the most failed JavaScript interview questions and provide easy-to-understand explanations and code examples.
What is the difference between null and undefined?
This is a classic JavaScript question that often catches developers off guard. Null and undefined are both JavaScript data types that are used to represent the absence of a value. However, they differ in their meaning. Undefined means a variable has been declared, but it has not been assigned a value. Null, on the other hand, is an assignment value that represents no value or an empty value.
Code Example:
let a;
console.log(a); // Output: undefined
let b = null;
console.log(b); // Output: null
What is hoisting in JavaScript?
Hoisting is a JavaScript mechanism where variables and function declarations are moved to the top of their scope before code execution. This means that you can use a variable or a function before it is declared.
Code Example:
console.log(a); // Output: undefined
var a = 10;
The above code is equivalent to the following code:
var a;
console.log(a); // Output: undefined
a = 10;
What is closure in JavaScript?
A closure is a function that has access to the outer function’s variables, even after the outer function has returned. This is possible because the inner function has a reference to the outer function’s variables. Code Example:
function outer() {
let a = 10;
function inner() {
console.log(a);
}
return inner;
}
let innerFunc = outer();
innerFunc(); // Output: 10What is the difference between synchronous and asynchronous code in JavaScript?
Synchronous code is executed in a sequence, one after the other. Asynchronous code, on the other hand, is executed out of sequence, with some code running in the background while the rest of the code continues to execute.
Code Example:
// Synchronous code:
console.log('Start');
console.log('Middle');
console.log('End');
// Output:
// Start
// Middle
// End
// Asynchronous code:
console.log('Start');
setTimeout(() => {
console.log('Middle');
}, 1000);
console.log('End');
// Output:
// Start
// End
// Middle
What is event bubbling in JavaScript?
Event bubbling is a phenomenon where an event that is triggered on a child element is also triggered on its parent elements. This is because events “bubble up” from the child element to its parent elements.
Code Example:
HTML:
<div id="parent">
<div id="child">
Click me
</div>
</div>
JavaScript:
let parent = document.querySelector('#parent');
let child = document.querySelector('#child');
child.addEventListener('click', () => {
console.log('Child clicked');
});
parent.addEventListener('click', () => {
console.log('Parent clicked');
});
// Output:
// Child clicked
// Parent clickedWhat is the difference between let, const, and var?
Let, const, and var are all used for declaring variables in JavaScript, but they differ in their scoping and hoisting behavior. Var declarations are hoisted to the top of their scope, while let and const declarations are not. Const declarations cannot be reassigned once they are declared, while let and var declarations can be reassigned.
Code Example:
var a = 10;
let b = 20;
const c = 30;
function example() {
console.log(a); // Output: undefined
console.log(b); // Output: ReferenceError: b is not defined
console.log(c); // Output: 30
var a = 1;
let b = 2;
const c = 3;
}
example();
console.log(a); // Output: 10
console.log(b); // Output: ReferenceError: b is not defined
console.log(c); // Output: ReferenceError: c is not defined
What is the difference between == and === operators?
The == operator checks if the operands are equal, but it performs type coercion if the operands are of different types. On the other hand, the === operator checks if the operands are equal and of the same type.
Code Example:
console.log(1 == '1'); // Output: true
console.log(1 === '1'); // Output: false
What is the difference between a function declaration and a function expression in JavaScript?
A function declaration is a function that is declared as a statement, and it is hoisted to the top of its scope. A function expression, on the other hand, is a function that is assigned to a variable, and it is not hoisted.
Code Example:
Function declaration:
function sayHello() {
console.log('Hello');
}
sayHello(); // Output: HelloFunction expression:
let sayHi = function() {
console.log('Hi');
};
sayHi(); // Output: HiIn conclusion, understanding these JavaScript concepts and being able to explain them in an interview is crucial for landing a job as a JavaScript developer. By mastering these concepts and practicing your coding skills, you can increase your chances of success in the highly competitive job market.
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Common JavaScript Interview Questions That Stump Job Candidates was originally published in Level Up Coding on Medium, where people are continuing the conversation by highlighting and responding to this story.
This content originally appeared on Level Up Coding - Medium and was authored by FardaKarimov
FardaKarimov | Sciencx (2023-05-12T16:19:03+00:00) Common JavaScript Interview Questions That Stump Job Candidates. Retrieved from https://www.scien.cx/2023/05/12/common-javascript-interview-questions-that-stump-job-candidates/
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