Javascript Questions

NaN property is a property of the global object that is used to represent the Not-a-Number value.

Number object is used to perform number operations.

Boolean object is used to perform boolean operations.

Falsy values are:

• 0
• ''
• null
• undefined
• NaN
• false

JavaScript data types are the types of values that JavaScript can store.

There are seven data types in JavaScript:

• Number
• String
• Boolean
• Undefined
• Null
• Symbol
• Object

The push method is used to add an element to the end of an array.

The window object is a global object that has the properties pertaining to the current DOM document

The document property of the window object has the DOM document and associated nodes and methods that we can use to manipulate the DOM nodes and listen to events for each node.

The window object is global, so it’s available in every part of the application.

JavaScript is a programming language that allows you to write applications that can run on the client side or server side

Undefined is a value that JavaScript assigns to variables that have not been assigned a value.

Null is a value that JavaScript assigns to variables that have been assigned a value but that value is null.

The === operator is used to compare two values and types. It returns true if both values and types are equal, and false if they are not equal.

There are three looping structures in JavaScript:

• For Loop
• While Loop
• Do While Loop

Break and continue statements are used to exit a loop or switch statement.

Break is used to exit a loop

Continue is used to skip the current iteration and continue to the next iteration.

There are three boolean operators in JavaScript:

• &&
• ||
• !

In Pass by value, function is called by directly passing the value of the variable as an argument. So any changes made inside the function does not affect the original value.

In Pass by Reference, Function is called by directly passing the reference/address of the variable as an argument. So changing the value inside the function also change the original value. In JavaScript array and Object follows pass by reference property.

The prototype is an object that is associated with every functions and objects by default in JavaScript, where function's prototype property is accessible and modifiable and object's prototype property is not visible

A callback is a function passed into another function as an argument, which is then invoked inside the outer function to complete some kind of routine or action.

A constructor is a special function that creates and initializes an object instance of a class. The purpose of a constructor is to create a new object and set values for any existing object properties.

The Document Object Model (DOM) is an API for HTML and XML documents. It is the programming interface for the HTML and XML documents.

Arrow functions are a new syntactic construct in JavaScript. They are a shorter way to write function expressions.

The ‘this’ keyword refers to the object that is currently executing the code. It is used to access properties and methods of an object.

Set object is used to perform set operations.

Variables are moved to the top of their scope before code execution

• Date;
• Math;
• String;
• Array.

Higher Order Functions are functions that take other functions as arguments or return other functions.

The strict mode is a way to make JavaScript more strict. It is used to prevent some common mistakes that can lead to JavaScript errors.

Implicit type coercion is a process in which a variable is automatically converted to a different type when it is assigned a value.

JavaScript is a dynamically typed language.

You can use try/catch blocks to handle exceptions

The try statement allows you to define a block of code to be tested for errors while it is being executed.

The catch statement allows you to define a block of code to be executed if an error occurs in the try block.

var

It's hoisted (always declared at top of the scope, global if none) and has function scope.

let

It has a block scope and is not redeclarable.

const

It has block scope, it's not reassignable and it's not redeclarable.

Memoization is an optimization technique used primarily to speed up programs that make repeated calculations.

Recursion is a technique in which a function calls itself. It is used to solve problems that can be solved by breaking down the problem into simpler sub-problems.

The unshift method is used to add an element to the beginning of an array.

Scope is the visibility of variables and functions.

Scope chain is the order in which the variables and functions are searched for a variable or function.

• Rest Parameter collects all remaining elements of an array or object into an array.
• Spread Operator expands collected elements such as arrays or objects into single elements.
• The spread syntax only does a shallow copy one level deep.
• Only the last parameter can be a rest parameter.

A Promise represents something that is eventually fulfilled. A Promise can be rejected, resolved or pending based on the operation outcome.

Object destructuring is a JavaScript feature that allows you to extract data from objects into distinct variables.

• Light Weight Scripting language
• Dynamic Typing
• Object-oriented programming support
• Functional Style
• Platform Independent
• Prototype-based
• Interpreted Language
• Async Processing
• Big Community
• Client-Side Validation

• Client-Side Security - Since JavaScript code is executed on the client-side, bugs and oversights can sometimes be exploited for malicious purposes. Because of this, some people choose to disable JavaScript entirely.
• Browser Support - While server-side scripts always produce the same output, different browsers sometimes interpret JavaScript code differently. These days the differences are minimal, and you shouldn't have to worry about it as long as you test your script in all major browsers.

Math object is used to perform mathematical operations.

Date object is used to perform date operations.

Hoisting is a JavaScript mechanism where variables and function declarations are moved to the top of their scope before code execution

Functions are fully hoisted, but varibles are semi-hoisted.

WeakSet is a collection of objects that are stored using a weak reference. This means that the objects in the set are not directly accessible from outside the set.

A closure is a stateful function that is returned by another function.

It has access to the parent scope, even after the parent function has closed.

The call() invokes the function and allows you to pass in arguments one by one.

The apply() invokes the function and allows you to pass in arguments as an array.

The bind() method creates a new function that, when called, has this keyword set to the provided value, with a given sequence of arguments preceding any provided when the new function is called.

Typeof operator is used to check the type of a variable.

Function declarations

• like vars, they will be automatically hoisted
• load before any other code

Function expressions

• not hoisted
• only loads when the interpreter reaches it

Generator functions are functions that can be paused and resumed at any point. They are used to create iterators.

An Immediately Invoked Function is a function that is automatically invoked when it is defined.

WeakMap is a collection of key-value pairs where the keys are stored using a weak reference. This means that the keys are not directly accessible from outside the map.

Map object is used to perform map operations.

setTimeout and setInterval functions are used to perform asynchronous operations.