1. What is Template literals in JavaScript?
Template Literals are used to Embide variable and Expressions Directly into String. Make the Code More Readable and Flaxible.
2. What is Hosting in JavaScript?
When Variable and Function are declared in JavaScript, and moved to the top of their Scope before the code execution. This is called Hosting.
console.log(a); // undefined
var a = 10;
Here the variable a is declared and Moved to the top of its Scope before the code execution. So, it returns undefined. this is called Hosting.
But in the case of let and const, it returns ReferenceError. Because Let and const are Hoisted in Temporal Dead Zone. It means that they are not executed before the line of code where they are declared.
console.log(a); // ReferenceError
console.log(b); // ReferenceError
let a = 10;
const b = 20;
3. What is Temporal Dead Zone
Temporal Dead Zone is a time between the variable creation and initialization Of the let and const variable. In this time, the variable is in the Temporal Dead Zone and cannot be accessed.
If you try to access a let or const variable before it has been initialized, JavaScript will throw a ReferenceError because the variable is in the Temporal Dead Zone.
console.log(a); // ReferenceError: Cannot access 'a' before initialization
let a = 5;
4. Type of Hosting in JavaScript?
In JavaScript, there are two types of Hosting.
1) Variable hosting
In variable Hosting the variable is moved to the top of its Scope before the code execution.
When we declare a variable using var keyword and Hosted to the top of its Scope. it returns undefined. While when we use let and const keyword, it returns ReferenceError.
2 ) function hosting
In JavaScript, function hoisting allows us to call the function before its declaration. It means that you can call the function before declared in the code.
sayHello(); // This works because the function is hoisted
function sayHello() {
console.log("Hello, World!");
}
- But in the case of Arrow function, it returns ReferenceError.
sayHello(); // ReferenceError: Cannot access 'sayHello' before initialization
const sayHello = () => {
console.log("Hello, World!");
};
4. Explain the difference between let, var and const in JavaScript?
The var is the oldest keyword to declare a variable in JavaScript. It has the Global scoped or function scoped. This means:
If you create a variable outside of a function, you can use it anywhere in your code.
If you create a variable inside a function, you can only use it within that function.
The let keyword is an improved version of the var keyword. It is introduced in the ES6 or EcmaScript 2015. These variables has the block scope. It can’t be accessible outside the particular code block ({block}).
The variable is only available inside the block {} where you define it.
The const keyword is used to declare a constant variable. It has the block scope. It can’t be reassigned. It must be initialized at the time of declaration.
const is similar to let, but with one big difference: once you assign a value to a const variable, you can’t change it later. Like let, const is block-scoped.
What is variable shadowing in JavaScript?
Inligal Shadowing
Read More: https://www.geeksforgeeks.org/variable-shadowing-in-javascript/
Question Related to JavaScript Variable Declaration
var can be re-declared and updated in the same scope.
let can be updated but not re-declared.
const cannot be re-declared or updated.
const a = 10;
a = 20; // Error: Assignment to constant variable.
What is the difference between a global and local variable?
A global variable is declared outside of a function and can be accessed anywhere in the code, while a local variable is declared inside a function and can only be accessed within that function.
What are some excellent rules for variable naming conventions?
Use clear and descriptive names: Choose names that clearly indicate the purpose of the variable, like
userNameorshoppingCart. A name should provide an immediate understanding of what data it holds.Avoid short or ambiguous names: Avoid using single letters like
a,b,c, or vague names likedataorvalue. These don't convey meaningful information about the variable’s content or usage and can make code harder to maintain.Be as descriptive and specific as possible: A good name is one that leaves no room for confusion. For example, using
currentUseris much more informative than justuserordata.Consistency across the team: Agree on naming conventions with your team. For instance, if a visitor on a website is referred to as
user, related variables should be namedcurrentUserornewUser, rather than something unrelated likecurrentVisitorornewLadyInRed.CamelCase convention: Variable names should always follow the camelCase convention, starting with a lowercase letter, and using capital letters for subsequent words (e.g.,
userProfile,totalAmount).Nouns for variables, verbs for functions: To differentiate variables from functions, variables should be named with nouns (e.g.,
userAge,orderItems), while functions typically start with verbs (e.g.,getUserInfo(),calculateTotal()).
In JavaScript, When should a constant be named in all caps?
In JavaScript, you should name a constant in all caps when the value is not meant to change throughout the program. This helps show that the value is "constant" and should stay the same.
For example, if you have a constant representing the number of days in a week, you could name it
DAYS_IN_WEEKto indicate that it should not be modified.
6 JavaScript Naming Conventions You Should Follow
Following proper naming conventions in JavaScript is key to writing clean, readable code. However, many developers might struggle with naming conventions. In this article, we’ll explore 10 best practices for naming variables, functions, constants, and other elements in JavaScript.
1. Naming Convention for Variables
JavaScript variable names are case-sensitive, meaning DogName, dogName, and DOGNAME are all treated as different variables. The recommended practice is to use camelCase for variable names.
Examples:
// Bad
var dogname = 'Droopy';
var DOGNAME = 'Droopy';
// Good
var dogName = 'Droopy';
2. Naming Convention for Booleans
- For boolean variables, use is or has as prefixes to indicate true/false values.
Examples:
// Bad
var open = true;
// Good
var isOpen = true;
var hasOwner = true;
3. Naming Convention for Functions
Function names should be camelCase and include descriptive verbs to clarify their purpose. For example, use getName() instead of just name() for a function that retrieves a name.
Examples:
// Bad
function retrieve() {
// code
}
// Good
function retrieveData() {
// code
}
function calculateTotal() {
// code
}
4. Naming Convention for Constants
Constants should be written in uppercase with underscore separation between words. This makes them stand out as non-changing values.
Examples:
// Bad
const daysInWeek = 7;
// Good
const DAYS_IN_WEEK = 7;
const MAX_ATTEMPTS = 3;
5. Naming Convention for Classes
Class names should be written in PascalCase (also known as UpperCamelCase) to distinguish them from regular functions.
Examples:
// Bad
class animal {
// code
}
// Good
class Animal {
// code
}
class UserAccount {
// code
}
6. Naming Convention for Components
For front-end frameworks like React, components are treated similarly to classes. Use PascalCase for component names to distinguish them from HTML elements.
Examples:
// Good
function DogCartoon(props) {
return (
<div>
<span>Dog Name: {props.dogName}</span>
<span>Owner Name: {props.ownerName}</span>
</div>
);
}
Can you declare multiple variables on one line?
- Yes, although the specification does not advise it for readability and consistency reasons. You can declare multiple variables on one line using either 'var', 'let', or 'const' by separating them with commas, but this is not the recommended approach.
// Example: one-line
let user = 'John',
age = 25,
message = 'Hello';
// The multiline variant is a bit longer, but easier to read:
let user = 'John';
let age = 25;
let message = 'Hello';
```
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