Java Script Interview Question |ES6 Feature React Interview Questions 1

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1). What is hoisting in JS?
Ans:-hoisting refers to the behavior where variable and function declarations are moved to the top of their containing scope
2). How it works?
actually declared in the code. This allows variables and functions to be used before they are declared in the code.
3). Does hoisting work with all the variables, and Why?

console.log(myVariable); // Output: undefined
var myVariable = 10;

function myFunction() {
console.log("Hello!");
}

myFunction(); // Output: "Hello!"



4). Diff. b/w "let" and "var"?
Ans:-var is a functional scope and let is block scope."var" keyword has been traditionally used in JavaScript to declare variables. Variables declared with "var" are function-scoped, which means they are accessible within the function they are declared in or throughout the global scope if declared outside of any function. "var" variables are also hoisted, which means they are moved to the top of their scope during the compilation phase.

Example:-

function example() {
var x = 10;
if (true) {
var y = 20;
console.log(x); // 10
}
console.log(y); // 20
}
example();
console.log(x); // ReferenceError: x is not defined

In the above example, both "x" and "y" are accessible within the function, even though "y" is declared inside the if statement.

"let": The "let" keyword was introduced in ECMAScript 6 (ES6) and provides block scoping. Variables declared with "let" are limited to the block in which they are declared (a block is typically denoted by curly braces {}). "let" variables are not hoisted, so they are only accessible after the point of declaration within their block.

5). What are the ES6 features you have used?
Ans:-ECMAScript 6 (ES6), also known as ECMAScript 2015, is a major update to the JavaScript language specification. It introduced several new features and enhancements to JavaScript, improving the language's syntax, functionality, and expressiveness. Here are some key features introduced in ES6:

let and const: The "let" and "const" keywords provide block-scoped variable declarations. "let" allows you to declare variables that are limited to a specific block, while "const" is used for declaring constants with values that cannot be re-assigned.

Arrow Functions: Arrow functions provide a concise syntax for defining functions. They have a shorter syntax compared to traditional function expressions and automatically bind the "this" value lexically.

Template Literals: Template literals allow for more expressive string interpolation. They use backticks (`) instead of single or double quotes and support embedded expressions within the string using the "${}" syntax.

Enhanced Object Literals: ES6 introduced enhancements to object literals, including the ability to define computed property names, shorthand property and method syntax, and the ability to define setters and getters.

Destructuring Assignment: Destructuring assignment allows for extracting values from arrays or objects and assigning them to variables using a concise syntax.

Default Parameters: Default parameter values can now be assigned directly in function declarations, providing a convenient way to specify fallback values for function arguments.

Rest Parameters: The rest parameter syntax allows functions to accept a variable number of arguments as an array, making it easier to work with a variable number of parameters.

Spread Operator: The spread operator allows for the expansion of elements in arrays, object literals, and function calls. It provides a concise way to copy arrays, merge objects, or pass multiple arguments to a function.

Classes: ES6 introduced a more standardized syntax for defining classes in JavaScript, providing syntactic sugar over the existing prototype-based inheritance.

Modules: ES6 introduced a native module system for organizing and reusing JavaScript code. Modules allow for the export and import of functions, objects, or values between different JavaScript files.

These are just a few of the many features introduced in ECMAScript 6. ES6 brought significant improvements to JavaScript, making the language more powerful, expressive, and developer-friendly.