Interview Faqs & Ans: Javascript, NodeJS, ReactJS, AngularJS

Create a simple javascript program and view the browser output, such as hello world, by placing script tags in the head or body sections of a page.

Explore how to call a JavaScript function by clicking a button in the browser, using an external script, the alert dialog, and an onclick event to run function f.

Identify the browser object model as the entity to interact with the browser, with window as the default browser object and alert as an example function.

Explore how the document object enables accessing and changing page content, reading input values and names, and using a click event to display the value via an alert dialog.

Explain that the window object is created automatically by the browser and is a browser object rather than a JavaScript object, with alert as a window method.

Explain how the JavaScript confirm function returns a boolean, displaying an OK window when true and invoking an alert with a cancel button when false, triggered by a button click.

Explain usage of the prompt function: F1 prompts for a name, stores it, and displays 'my name is [input]' in an alert. Canceling yields null and 'my name is null'.

Demonstrates how the open function is invoked by a button click to open content. Clicking triggers open to run hello world, revealing the result on screen.

Explore how to navigate browser history with the JavaScript history object on the window, using forward, back, and go to move between pages.

Explore JavaScript program validity and execution, including line and block comments, and how the document object renders content in the browser.

Investigate whether document.write can use a function's return value as its parameter by showing a function that returns a string and is passed to document.write.

Explain dynamic type language by showing that JavaScript does not require explicit type declarations; the engine dynamically assigns types so a variable can hold numbers, strings, or other values.

Evaluate JavaScript statements about undefined values, regular expressions, groups, and non-permitted constructs to determine which concepts truly belong to JavaScript.

Explore JavaScript equality operators: the '==' checks equality, while '===' requires both equality and the same type.

Explore how JavaScript creates objects without classes: using object literals, the Object constructor, and the new keyword, plus object constructors and dot notation to access properties.

Discover how to create arrays in JavaScript using literals, the new operator, and constructor-based approaches. Learn how a for loop iterates and prints array elements.

The plus operator in JavaScript switches between numeric addition and string concatenation; 81 + 82 + '85' yields 16385, while '81' + 82 + 85 yields '818285'.

Explain client-side JavaScript and server-side JavaScript, outlining how JavaScript runs in the browser as an interpreted language with embedded data on pages and predefined objects.

Clarify what undefined means for a variable. Contrast it with a value explicitly set by a keyword, introducing the concept of a non-value.

Explore the javascript boxes and the alert box, highlighting the different box options available in javascript as mentioned in the caption.

Evaluate if navigator.appVersion should be used to detect the operating system, noting it can reveal the OS rather than the app version.

Demonstrates how to change the page background by assigning document.body.bgColor to a color, and shows the background turning pink.

Explain the difference between undefined and not defined in JavaScript: a declared variable with no value yields undefined, while a not defined variable is not declared.

JavaScript private methods are memory inefficient since each instance gets its own copy, so avoid private methods unless necessary.

Explore the concept of closure: a function defined inside another function retains access to outer variables, returning an inner function that increments a counter across calls.

Define the add function using nested anonymous functions to sum the inputs 1, 2, and 3, producing the final result of 6.

Explore three ways to empty an array in JavaScript: assign [], set to zero, or use a method that clears contents using the array length, demonstrated with A and B.

The delete operator targets object properties, not global or local number variables. The example shows that X, a global number, remains after the delete attempt, printing 1.

Explore how the delete operator removes a property from an object. See the resulting output showing the property deleted and the value as undefined.

Explore whether the delete operator removes a prototype property in JavaScript. The lecture demonstrates deleting an own property like employee.company and attempts to delete a __proto__ property, comparing outcomes.

Demonstrate the delete operator removing the element at index 3 in an array, while the length property stays unchanged; the program prints the array content and its length.

The lecture analyzes a program that combines a boolean true with numbers and strings, showing true becomes 1 in numeric contexts and string concatenation can produce 1 and 2.

Evaluate the JavaScript snippet to determine the output, fix an undefined reference by declaring a separate variable, and note the function returns a number via an anonymous function.

Clarify the difference between two statements, showing that the function foo is defined at runtime while the function bar is defined at Botstein.

Discover how function scope and undefined values affect the output of JavaScript code, illustrated by salary usage, console.log, and a variable defined in context.

Explain how typeof var1 === 'object' can mislead when values are null, arrays, or functions, and show how explicit null checks distinguish objects from non-objects.

Analyze how JavaScript handles output, scoping, and undefined versus defined variables when using var, including how strict mode reveals undefined references and global scope.

Explain how strict mode enforces stricter parsing and error handling in JavaScript, making debugging easier, preventing accidental globals, and throwing on references to undefined or attempts to delete non-configurable properties.

Demonstrates the output of a code snippet involving typeof NaN and equality checks, showing one statement evaluates to true while the other is false because NaN's type is number.

Explains how synchronous logs print first; setTimeout with zero delay queues functions for the next tick, so they log after current calls as the event loop processes the queue.

Create a function to determine whether a string is a palindrome by converting it to lower case, reversing the content, and comparing it to the original.

Implement the mul function to support both direct and curried calls, yielding 6 for either mul(2,3) or mul(2)(3) by checking arguments length and using the supplied values.

Analyze how a for loop creates buttons and binds onclick. The code always prints 5 on the console due to execution context, variable objects, activation object, and internal scope property.

Analyze code snippets to reveal array operations that determine output: reverse mutates the array and returns a reference, while push and concat build arrays, and minus-one subscripts access last element.

Analyze how JavaScript coerces types in plus operations by mixing strings and numbers, showing outputs like 2 3 3 and 0 3 through unary plus and minus.

Explain how the output of a program is determined by boolean evaluation of the or and and operators, including short-circuit behavior and expression return values, with numeric examples.

This lecture explains how the triple equals (===) operator compares both type and value, versus the double equals (==) that compares values, with examples showing true or false.

Determine the program output as 6 5 4. Explain that JavaScript implicitly stringifies object values when assigning to an object property, producing a string representation of the objects.

Explore how a recursive function computes factorial by calling itself with n minus one until the base case returns one, producing 3628800 as the final output.

Explore closures in JavaScript: a function returns another function that closes over outer variables. The inner function accesses outer y and prints its value, illustrating scope preservation.

Explain how extracting a method from an object sets this to the global window, producing undefined and ABC_EFB, and how binding fixes the context to yield the expected output.

Analyze a JavaScript try-catch snippet that throws an error and logs values from 1, undefined, and 2, illustrating variable hoisting and scope behavior around catch and outer code.

Explore why the given JavaScript code outputs undefined rather than 21 or 20, due to variable initialization and hoisting within a function.

Explain shallow versus deep copy in JavaScript object cloning, showing how nested objects remain shared and how mutations affect both the original and the clone through console outputs.

The lecture shows a loop-based program that prints 0 through 5 and explains how using let instead of var enforces block scope, making g visible only within its block.

Evaluate the output of two code statements by applying relational operators on numbers, producing true or false values. See how true or false results influence conditional logic in programming tasks.

this lecture traces a six-slot javascript array x with empty indices, showing undefined outputs for unset slots and how map operations affect the resulting outputs.

Learn how event bubbling handles the event at the innermost element first and then propagates outward, while event capture handles the outermost element first and then moves inward.

Use the close method to close the current window in JavaScript, and ensure the command targets the window object rather than another JavaScript object.

Explain the concepts of let and var, contrasting block-scoped let with var's global scope, and show how let limits scope in loops and conditionals while addressing global object behavior.

Explain the delegation model, where a single handler manages events for many elements. It applies one pattern to multiple nodes and uses a listener to match events on child elements.

Describe negative infinity as a value lower than any other number, a static property accessible on the global object without creating objects, derived by dividing a number by zero.

Evaluate true or false statements about infinity, negative infinity, and related arithmetic, including zero and division by infinity, to boost interview readiness for javascript and nodejs topics.

Investigate whether Node.js supports event looping and how this applies to building a single application.

Explore api functions in nodejs, distinguishing asynchronous nonblocking functions from synchronous blocking functions to understand when to use each for efficient server-side code.

Explore how Node.js uses error-first callbacks to pass errors and data, and learn to inspect the first argument when something goes wrong.

Explore what nonblocking APIs mean in JavaScript, highlighting asynchronous behavior and event notification mechanisms that deliver responses for prior API calls.

Explore options to avoid callback functions, including modularization by breaking callbacks into independent functions, adopting promises, and using yield generators to manage asynchronous code.

Explore the control flow segment that runs between asynchronous function calls, and learn how it orders execution, collects data, limits concurrency, and triggers the next function.

Identify functions that run asynchronously with the event loop, including nonblocking input/output operations and heavy computations.

Identify tools that catch common errors during static analysis and enforce a given style guide within JavaScript, NodeJS, ReactJS, and AngularJS projects.

the lecture explains that a zero-delay setTimeout queues a callback, producing the output C then B, and that setImmediate runs after io events for the same output with faster performance.

Node.js runs as a single-thread process and does not expose child threads; it uses background threads for asynchronous I/O and does not block the main event loop.

Discover how unhandled exceptions reach the process level in Node.js and how the domain layer isolates error handling to prevent undefined state, enabling safer recovery.

Discover how Node.js uses the cluster model to run multiple processes that share the same port, enabling deployment on multi-core systems beyond the default single-core execution.

Explains that the first argument to a callback handler is an optional object, often null or undefined when there is no error, guiding early error checks before proceeding.

Explain promises and how they handle async operations, with an example showing a string printing to standard output after 100 milliseconds and using error handling.

Explore how to secure cookies against cross-site scripting by using HttpOnly and Secure attributes, and by setting cookie flags to mitigate such attacks.

Identify the problem: the catch discards the error and execution continues, returning a new increment value, even though the exception hasn't halted execution.

Node.js and Ajax serve different purposes: Ajax dynamically updates a page section without reloading the entire page, while Node.js is used for developing client-server applications.

Explain how chaining connects the output of one stream to another in Node.js, creating a chain of multiple stream operations.

Explain how nodejs streams enable reading from a source and writing to a destination. Describe four types: reading, writing, both, and a duplex with input-based computations.

Explain exit codes in Node.js and how they end a process, with examples of uncaught exceptions, fatal errors, and the internal exception handler.

Explore Node.js globals, focusing on the global namespace object that contains all objects, the process global for application information, and the buffer class for handling binary data.

Explore whether consistent style is important in nodejs, and show how a standard, uniform approach helps team members modify projects easily and avoid adjusting to new styles.

Explore the difference between AngularJS and NodeJS, clarifying their roles in web application development and runtime system.

Explore the difference between using var and not using var when dealing with variables, including how values are stored and printed in an API context.

Compare global and local installation of dependencies in npm: global installs serve command-line interface tools in npm's global directory; local installs reside in the project's node_modules and are importable.

explain why we execute the command to verify globally installed dependencies and ensure the development environment is correctly configured.

Explore how package.json defines a node package's metadata, including name, version, description, homepage, author, dependencies, entry point, and keywords, with npm automatically installing dependencies.

Learn how to uninstall a dependency with npm using the command, and how to update your dependency with npm.

Explain blocking code and how callbacks prevent it. Learn that the callback function gets called when the corresponding event is triggered.

Import the events module to create an event emitter object and bind handlers with on. Emit events to trigger listeners, and remove listeners with removeListener; no event fires.

Explain how the Buffle class is a global class accessible without importing, and its relation to an array of integers with a raw memory allocation outside the heap.

Connect the output of one stream to another using piping. Learn how to read from a file and write to another file via streams.

Understand why we use the node fs module for file-based operations, contrasting buffer-based and asynchronous callbacks with synchronous methods that can block execution.

Explore the purpose of file open flags for read and write operations, including read-only, write-only, read-write, create, truncate, append, and exclusive options, and how they affect file existence and performance.

Explore how streams emit events, including data available to read, no more data to read, data being received or written, and the finish event when data is flushed.

Discover why the fs.open() call opens a specific file by passing the file name as a string, the mode, and a callback function.

Learn how to use fs.read() in Node.js by passing a file descriptor, a buffer, offset, length, and position, and handling the callback with bytes read.

Explains how to use Node.js fs calls to manage files and directories, including fs.close, fs.stat, fs.ftruncate, fs.unlink, fs.mkdir, fs.rmdir, and fs.readdir, with practical usage briefly described.

Explain __filename and __dirname by showing how __filename gives the executed file’s name and absolute path, while __dirname returns the directory of the currently executing script.

Explain how setTimeout, clearTimeout, and setInterval schedule callbacks after delays or repeatedly, returning an opaque timer id used to clear the timer, with granularity and load affecting max 24.8 days.

Explain the console object for printing to standard out and standard EDR, and the process object for retrieving information about the current process and related events.

React is a JavaScript UI library from Facebook for building interactive, reusable components in web and mobile apps, with a virtual DOM, JSX, and server-side rendering.

Explore how components use props to display content by building a class component that renders a welcome message and mounts with ReactDOM.render into the DOM.

Explain JSX and how it extends ECMAScript with a React-like syntax, transformed by Babel into JavaScript for use with React code.

Understand how React components follow a lifecycle, with mounting, updating, and unmounting phases, using will and did methods to run code before and after changes to props or state.

Handle events in React by using camelCase event names like onClick and function references, and pass your handler in braces. Use event.preventDefault() to stop default actions instead of returning false.

Explain flux as an application architecture for unidirectional data flow in JavaScript applications. Clarify that flux is not a framework or library but a design that complements unidirectional data flow.

Explain refs in React as a way to store references to elements or components, and discuss their use for focus management, media playback, and triggering animations or third-party DOM libraries.

Explain stateless components and when to use state, showing how they render from props without mutating state directly, and how to manage state with plain functions or JSX components.

The dom defines the document structure and content; the virtual dom is a lightweight abstraction of dom objects, used to optimize updates without touching the real dom.

Identify the disadvantages of reactjs, including a steep learning curve for beginners, major configurations to integrate with traditional mvc frameworks, and potential challenges with search engine optimization.

Differentiate controlled and uncontrolled components in forms. Controlled components receive values as props and use callbacks to update them, while uncontrolled components rely on the DOM to manage form data.

Compare functional components with class components in React, highlighting that functional components are simple stateless JavaScript functions, while class components use class syntax and define methods.

Higher order components are a function that takes a component as input, a modern technique in React that emerges from its compositional nature to handle logic.

ReactJS, a library by Facebook for building user interfaces, enables fast, scalable single page applications; AngularJS, a framework with multiple versions, contrasts with Vue.js as a rapidly adaptable option.

Explain how arrow functions handle this in callbacks to prevent this-related bugs and make function behavior easier to predict.

Explain React component lifecycle methods in detail, including get default props, will mount, did mount, will receive props, should update, did update, and unmount, with emphasis on reusable components.

Explain that browsers cannot read JSX directly, and show how components are building blocks of applications, split into independent pieces that don't affect the rest of the user interface.

Explain how props act as shorthand for properties in React, ensuring immutable data and directional data flow, enabling components to render dynamically generated data.

Explain states: the heart of React, the source of data that must stay simple. Make states mutable objects that determine rendering and behavior, form components, and are accessed via this.state.

Explore how synthetic events in React unify cross-browser behavior through a single API, ensuring consistent properties across different browsers.

Explain controlled versus uncontrolled components, where controlled components derive data from the parent via props and callbacks, while uncontrolled components rely on the DOM and refs to access current values.

Explain pure components as the simplest and fastest components. Show how they replace any component that only has other function, boosting code simplicity in the application.

Explain how keys identify unique virtual DOM elements to drive the UI, enabling React to optimize rendering by recycling existing elements and improving performance.

Explore the major problems of the MVC framework, including slow performance, memory overhead, and inefficiencies that impact application scalability.

Explore Redux, a predictable state management library for JavaScript apps. Use a store to hold the app state, with actions and reducers updating it, while views display the data.

Reducers are pure functions that specify how the application's state changes in response to an action. They return a new or unchanged state based on the action type.

Compare flux and redux: flux uses multiple stores with a singleton dispatcher and mutable state, while redux uses a single immutable store and no dispatcher.

Explain React Router as a powerful routing library built on React that adds new screens and flows, keeps data in sync, and provides a simple API for defining multiple routes.

Compare conventional routing and React routing, showing that conventional routing loads a new page per view while React routing updates the history attribute on a single page.

Explain the switch keyword in React Router v4, showing how it renders only a single route among many by matching the first route in order and bypassing the rest.

Compare ES5 and ES6 approaches to React components by illustrating auto binding, initial state with getInitialState, defaultProps, displayName, and event handler binding versus manual binding.

Explain how the virtual dom represents a nested plain JavaScript object, how React renders elements via createElement, and how custom components produce elements.

Explore React lifecycle methods that govern a component from creation to cleanup. Classify mounting, updating, and unmounting phases, including componentWillMount, componentDidMount, componentWillReceiveProps, componentWillUnmount, and shouldComponentUpdate.

Explain how keys in React identify unique DOM elements to optimize rendering by recycling elements, using a follower-count example to demonstrate preserving order and performance.

Compare setState and forceUpdate in React: setState updates state and triggers rendering via lifecycle methods; forceUpdate overrides rendering and bypasses shouldComponentUpdate; use setState unless a deliberate bypass is needed.

Explain pure functional components and contrast them with traditional class components in React, showing how pure functions replace stateful components and avoid constructors and lifecycle methods.

Learn how shouldComponentUpdate controls rendering, confirming that a component renders only when its id changes, and how the update feature affects render behavior.

Explore AngularJS as a framework to build large-scale, high-performance web applications with a model–view–controller architecture that keeps code maintainable and cross-browser compatible.

Explore how AngularJS data binding automatically synchronizes data between the model and the view, illustrating the core mechanism behind AngularJS data binding.

clarifies AngularJS scope by describing scopes as objects that refer to the model and act as glue between the controller.

Explore AngularJS controllers as JavaScript functions bound to a scope, and learn how they operate on data to determine which view updates to reflect the model.

Explain how AngularJS services work as singleton objects, instantiated only once, and used to handle requests and object calls within an app.

Explore how AngularJS filters select a subset of items from an audit and display items from a list based on defined criteria.

Explore how AngularJS directives mark DOM elements with attributes to drive custom widgets. See how these directives enable model interactions and bind operations within AngularJS apps.

Explore how templates in AngularJS connect controllers to views, and how a single file or multiple views on one page can use partials.

Explain routing in AngularJS as switching views, with a controller selecting the active view based on business logic.

Learn how AngularJS boot process loads the document, creates the angular global object, registers and connects controllers, runs them, and renders the page with model data.

Explain the ng-app directive and how it defines the AngularJS application and marks the start of the app.

Explain ng-bind directive in AngularJS, showing how it binds the model to the view and updates the displayed data when the controller modifies the model.

Explain how the ng-controller directive uses a controller object with attributes and functions to manage data flow in an AngularJS application, with scope binding to the controlled app.

Discover how the angularjs javascript library integrates with html by mounting to a root element on a web page. Learn the basics of wiring the library into your html structure.

Explain integrating a pure JavaScript library into an Angular app by removing the library and injecting a script tag into the head or body, then appending to the root element.

Explore how the ng-init directive initializes application data by assigning initial values to variables used in the app.

Explain the ng-repeat directive and how it repeats elements for each item in a collection.

Explain how AngularJS expressions are used to bind complex expressions and outputs, and understand their behavior.

Explain how uppercase and lowercase filters convert text in templates, with examples of all-capital outputs and applying uppercase expressions in javascript contexts.

Explain using the currency filter and currency pipe to format numbers in JavaScript and AngularJS, review format specs, and apply numeric expressions.

explain orderby filter, focusing on sorting data by id based on provider. the example shows how to order subjects by mocs as used by mocs.

Explore how ng-disabled, ng-show, ng-hide, and ng-click control element availability, visibility, and click interactions in Angular directives, with examples of updating models and responding to user actions.

Explain how the angular model works and how to create angular models, including an example of declaring an application main monument using the angular dog Maryan function.

Learn to validate data in AngularJS by using form declarations and tracking states such as $dirty and $invalid to manage validations and enable specific checks.

Explain the ng-include directive and how it embeds content, focusing on practical use for a non-technical audience.

Learn how to get data on the server by formatting data, interfacing with a database, and enabling server-side data access and auditing.

Explore rootScope as a special javascript object that acts as the top-level scope, linking controllers and enabling data access via the scope object.

Explore the difference between service and factory in AngularJS, learn how to define and assign a service, and how a factory creates reusable services.

Discover how AngularJS extensibility works by creating custom directives to extend or replace existing elements. Learn how Bootstrap matches elements and how directive scope shapes the linking behavior.

Identify the types of components on which we can create custom directives and describe how a matching condition activates them.

Explain internationalization and translation by supporting locales like en-us and hi-in, and formatting currencies and numbers according to user location and browser settings.

Learn the basic steps to unit test an AngularJS filter, including dependency injection, using mocks, obtaining test data, and asserting expectations, supported by open source examples.

Track the maximum number of concurrent watches to reduce memory usage and boost performance by limiting watchers and monitoring the watch count.

Explain how ng-show/ng-hide and ng-if differ: ng-show/ng-hide toggles visibility, while ng-if inserts or removes the element from the DOM based on the condition.

Learn how the digest cycle in angular compares old and new scope model values, when it triggers automatically, and how to manually trigger it with the $apply function.

Explain the use and placement of semicolons to ensure a scope variable has a single binding, and how this checks candidate understanding of variable bindings in JavaScript.

Explore the difference between one-way binding and two-way binding, and how a binding updates the value when it is reassigned, highlighting practical implications in code.

Trigger $scope.$apply triggers the angular digest cycle, evaluating all changes and applying updates to altered and external variables, a core function that should not be invoked directly.

Explore how an angular factory uses $q promises and deferred objects to create an asynchronous service that acts as a health care provider.

Define how your directive is used by configuring its declaration to match attributes, elements, or classes, and combine restrictions as needed.

Explore when to use an element versus an attribute in a component template, showing how an element controls the template and how an attribute decorates existing elements with new functionality.

Demonstrate how the singleton pattern restricts a class to a single instance, reusing the same object instead of creating new ones, to manage memory.

Explain how interceptors manage request and response flows, including headers, within a factory-registered component, and how they facilitate handling different responses.