Mukesh Machinery Store And Jindal Pipe Store Interview Questions and Answers

JavaScript has three main types of variables: var, let, and const, each with different scopes and mutability.

• var: Function-scoped or globally-scoped. Example: var x = 10;

• let: Block-scoped and can be updated. Example: let y = 20;

• const: Block-scoped and cannot be reassigned. Example: const z = 30;

Closures are functions that retain access to their lexical scope, even when executed outside that scope.

• A closure is created when a function is defined inside another function.

• Closures can access variables from their parent function's scope.

• They help in data encapsulation and maintaining state.

• Example: function outer() { let count = 0; return function inner() { count++; return count; }; }

• Closures are commonly used in callbacks and event handlers.

Hoisting is a JavaScript mechanism where variable and function declarations are moved to the top of their containing scope.

• Variable and function declarations are hoisted to the top of their scope during the compilation phase.

• Only declarations are hoisted, not initializations.

• Function declarations take precedence over variable declarations.

Closures are functions that have access to variables from their outer scope even after the outer function has finished executing.

• Closures allow functions to access variables from their parent function even after the parent function has returned.

• They help in maintaining state in JavaScript.

• Closures are created whenever a function is defined within another function.

Promises in Node.js are objects representing the eventual completion or failure of an asynchronous operation.

• Promises are used to handle asynchronous operations in a more readable and manageable way.

• They can be in one of three states: pending, fulfilled, or rejected.

• Promises can be chained together using .then() to handle success or failure.

• They help avoid callback hell and make code more maintainable.

• Example: const myPromise = new Promise((resolve, reject) => { ... });

Callbacks are functions passed as arguments to other functions, to be executed later.

• Callbacks are commonly used in asynchronous programming in Node.js.

• They allow functions to be executed after another function has finished its execution.

• Callbacks can be used to handle events, make API calls, or perform other tasks asynchronously.

• Example: fs.readFile('file.txt', (err, data) => { console.log(data); });

Convert decimal to binary without using inbuilt functions

• Create an empty array to store binary digits

• Use a while loop to divide the decimal number by 2 and store the remainder in the array

• Reverse the array to get the binary representation