Relevantz Technology Services Senior Angular Developer Interview Questions and Answers

Singleton design pattern restricts the instantiation of a class to one object.

• Ensures only one instance of a class exists

• Provides a global point of access to that instance

• Used when only one instance of a class is needed throughout the application

• Example: Database connection manager

Event loop is a mechanism that allows non-blocking I/O operations in a single-threaded environment.

• Event loop is used in programming languages like JavaScript and Python.

• It manages the execution of multiple tasks by prioritizing them based on their priority level.

• It continuously checks for new events and executes them in a loop.

• It allows for efficient handling of I/O operations without blocking the main thread.

• It is co...read more

let, var and const are used to declare variables in JavaScript with different scoping rules and mutability.

• let and var are used to declare variables that can be reassigned later, but var has function scope while let has block scope.

• const is used to declare variables that cannot be reassigned and have block scope.

• Using const does not mean the value is immutable, only the variable reference is.

• let and const were introduc...read more

React lifecycle, Fragment vs React.Fragment, React.PureComponent

• React lifecycle consists of mounting, updating, and unmounting phases

• Fragment is a shorthand for React.Fragment, used to group multiple elements

• React.PureComponent is a class component that implements shouldComponentUpdate method for performance optimization

JavaScript hoisting and differences between let, var and const.

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

• Var declarations are hoisted to the top of their scope, while let and const declarations are not.

• Var can be redeclared and reassigned, let can be reassigned but not redeclared, and const cannot be reassigned or redeclared.

• Using const is recommend...read more

Prevent rerendering of a child component in React

• Use shouldComponentUpdate() lifecycle method

• Use React.memo() to memoize functional components

• Use PureComponent instead of Component

• Pass props as a callback function to avoid unnecessary re-renders

• Use React.PureComponent for class components

• Use React.memo() for functional components