Tuesday, June 18, 2024

Javascript Coding Questions For Interview

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What Are The Pros And Cons Of Promises Over Callbacks

JavaScript Interview Questions and Answers | Top 70 JavaScript Interview Questions | Great Learning

Below are the list of pros and cons of promises over callbacks,


  • It avoids callback hell which is unreadable
  • Easy to write sequential asynchronous code with .then
  • Easy to write parallel asynchronous code with Promise.all
  • Solves some of the common problems of callbacks
  • Cons:

  • It makes little complex code
  • You need to load a polyfill if ES6 is not supported
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    Q27 Explain The Procedure Of Document Loading

    Topic: JavaScript


    Loading a document tells preparing it for further execution on the system. The document loads instantly on the browser when there is a running document on the system. The application permits the JavaScript engine to do dual tasks:

    • Search for all the properties, provided to the object.
    • Involve all the property values, used in the content that is being served for the page about to load.

    To load the document instantly, it is a great practice to add the < script> tag inside the < body> tag. The below program loads the document automatically and returns the OS details of the user:

    < html> < body> < H1> JavaScript used< /H1> < script> < !-- Comments to hide js in old browsers        document.write        document.write        // end of the comment section --> < /script> < /body> < /html> 

    How Do You Decode Or Encode A Url In Javascript

    encodeURI function is used to encode an URL. This function requires a URL string as a parameter and return that encoded string.decodeURI function is used to decode an URL. This function requires an encoded URL string as parameter and return that decoded string.

    Note: If you want to encode characters such as / ? : @ & = + $ # then you need to use encodeURIComponent.

    leturi="employeeDetails?name=john& occupation=manager" letencoded_uri=encodeURI letdecoded_uri=decodeURI 

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    Which One Is Not A Difference Between Typeof And Instanceof

    • typeof returns a type and instanceof returns a boolean.
    • instanceof requires TypeScript and typeof does not.
    • typeof takes the variable name on the right, and instanceof takes a value instead of on the left and right.

    The answer is B, as neither of them requires TypeScript and both are native to JavaScript.

    What Is A Service Worker

    Code Interview Question: Functional FizzBuzz in JavaScript

    A Service worker is basically a script that runs in the background, separate from a web page and provides features that don’t need a web page or user interaction. Some of the major features of service workers are Rich offline experiences, periodic background syncs, push notifications, intercept and handle network requests and programmatically managing a cache of responses.

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    How Do You Trim A String At The Beginning Or Ending

    The trim method of string prototype is used to trim on both sides of a string. But if you want to trim especially at the beginning or ending of the string then you can use trimStart/trimLeft and trimEnd/trimRight methods. Let’s see an example of these methods on a greeting message,

    vargreeting="   Hello, Goodmorning!   " console.log // "   Hello, Goodmorning!   "console.log) // "Hello, Goodmorning!   "console.log) // "Hello, Goodmorning!   "console.log) // "   Hello, Goodmorning!"console.log) // "   Hello, Goodmorning!"

    Q25 What Are The Ways To Define A Variable In Javascript

    The three possible ways of defining a variable in JavaScript are:

    • Var The JavaScript variables statement is used to declare a variable and, optionally, we can initialize the value of that variable. Example: var a =10 Variable declarations are processed before the execution of the code.
    • Const The idea of const functions is not allow them to modify the object on which they are called. When a function is declared as const, it can be called on any type of object.
    • Let It is a signal that the variable may be reassigned, such as a counter in a loop, or a value swap in an algorithm. It also signals that the variable will be used only in the block its defined in.

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    What Is A Void Operator

    The void operator evaluates the given expression and then returns undefined. The syntax would be as below,

    voidexpression voidexpression 

    Let’s display a message without any redirection or reload

    < ahref="javascript:void)">   Click here to see a message< /a> 

    Note: This operator is often used to obtain the undefined primitive value, using “void”.

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    Give An Example Where Do You Really Need Semicolon

    Tricky JavaScript Interview Questions and Answers

    It is recommended to use semicolons after every statement in JavaScript. For example, in the below case it throws an error “.. is not a function” at runtime due to missing semicolon.

    // define a functionvarfn=)) 

    and it will be interpreted as


    In this case, we are passing the second function as an argument to the first function and then trying to call the result of the first function call as a function. Hence, the second function will fail with a “… is not a function” error at runtime.

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    What Are The Modules In Nodejs

    Modules are like JavaScript libraries that can be used in a Node.js application to include a set of functions. To include a module in a Node.js application, use the require function with the parentheses containing the module’s name.

    Node.js has many modules to provide the basic functionality needed for a web application. Some of them include:

    Core Modules

    Includes classes, methods, and events to create a Node.js HTTP server


    Includes utility functions useful for developers

    Includes events, classes, and methods to deal with file I/O operations

    Includes methods for URL parsing

    query string

    Includes methods to work with query string


    Includes methods to handle streaming data


    Includes methods to compress or decompress files

    What Is A Proper Tail Call

    First, we should know about tail call before talking about “Proper Tail Call”. A tail call is a subroutine or function call performed as the final action of a calling function. Whereas Proper tail call is a technique where the program or code will not create additional stack frames for a recursion when the function call is a tail call.

    For example, the below classic or head recursion of factorial function relies on stack for each step. Each step need to be processed upto n * factorial

    functionfactorialreturnn*factorial }console.log) //120

    But if you use Tail recursion functions, they keep passing all the necessary data it needs down the recursion without relying on the stack.

    functionfactorialreturnfactorial }console.log) //120

    The above pattern returns the same output as the first one. But the accumulator keeps track of total as an argument without using stack memory on recursive calls.

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    Question #: Using A Closure Within A Loop

    Closures are sometimes brought up in an interview so that the interviewer can gauge how familiar you are with the language, and whether you know when to implement a closure.

    A closure is basically when an inner function has access to variables outside of its scope. Closures can be used for things like implementing privacy and creating function factories. A common interview question regarding the use of closures is something like this:

    Write a function that will loop through a list of integers and print the index of each element after a 3 second delay.

    A common implementation Ive seen for this problem looks something like this:

    If you run this youll see that you actually get the 4 printed out every time instead of the expected 0, 1, 2, 3 after a 3 second delay.

    To correctly identify why this is happening it would be useful to have an understanding of why this happens in JavaScript, which is exactly what the interviewer is trying to test.

    The reason for this is because the setTimeout function creates a function that has access to its outer scope, which is the loop that contains the index i. After 3 seconds go by, the function is executed and it prints out the value of i, which at the end of the loop is at 4 because it cycles through 0, 1, 2, 3, 4 and the loop finally stops at 4.

    There are actually a few ways of correctly writing the function for this problem. Here are two of them:

    What Is The Use Of History Object

    Pin on Programming Tips

    The history object of a browser can be used to switch to history pages such as back and forward from the current page or another page. There are three methods of history object.

  • history.back – It loads the previous page.
  • history.forward – It loads the next page.
  • history.go – The number may be positive for forward, negative for backward. It loads the given page number.
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    Top Javascript Coding Interview Questions And Answers

    The Indeed Editorial Team comprises a diverse and talented team of writers, researchers and subject matter experts equipped with Indeed’s data and insights to deliver useful tips to help guide your career journey.

    Knowing how to answer common JavaScript coding interview questions can help you get a developer job. Regardless of the specific developer role you are after, showing your JavaScript proficiency can increase the odds of you succeeding. Properly answering JavaScript-related questions is a valuable skill, but it takes research and practice. In this article, we discuss some of the most common JavaScript interview questions and their answers.

    How Do You Reuse Information Across Service Worker Restarts

    The problem with service worker is that it gets terminated when not in use, and restarted when it’s next needed, so you cannot rely on global state within a service worker’s onfetch and onmessage handlers. In this case, service workers will have access to IndexedDB API in order to persist and reuse across restarts.

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    Q: Explain The Difference Between Objectfreeze Vs Const

    Topic: JavaScriptDifficulty:

    const and Object.freeze are two completely different things.

    • const applies to bindings . It creates an immutable binding, i.e. you cannot assign a new value to the binding.
    const person =  let animal =  person = animal  // ERROR "person" is read-only
    • Object.freeze works on values, and more specifically, object values. It makes an object immutable, i.e. you cannot change its properties.
    let person =  let animal =  Object.freeze person.name = "Lima"  //TypeError: Cannot assign to read only property 'name' of objectconsole.log 

    How Do You Create Specific Number Of Copies Of A String

    Coding Interview – How to reverse a string in JAVASCRIPT

    The repeat method is used to construct and return a new string which contains the specified number of copies of the string on which it was called, concatenated together. Remember that this method has been added to the ECMAScript 2015 specification.Let’s take an example of Hello string to repeat it 4 times,

    "Hello".repeat // 'HelloHelloHelloHello'

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    What Are All The Loops Available In Javascript

    The available loops available in JavaScript are given below:-

    -For loop statement:-

    The JavaScript For loop is the same as for loops of Java and C. For loop continues until a specified condition evaluates to false.


    2-While loop:-

    A while statement executes its statement until a specified condition evaluates to true, a while statement looks like as follows:-

    Ex:- while

    So this is called variable typing. This concept of JS is similar to Java.

    What Is Minimum Timeout Throttling

    Both browser and NodeJS javascript environments throttles with a minimum delay that is greater than 0ms. That means even though setting a delay of 0ms will not happen instantaneously.Browsers: They have a minimum delay of 4ms. This throttle occurs when successive calls are triggered due to callback nesting or after a certain number of successive intervals.Note: The older browsers have a minimum delay of 10ms.Nodejs: They have a minimum delay of 1ms. This throttle happens when the delay is larger than 2147483647 or less than 1.The best example to explain this timeout throttling behavior is the order of below code snippet.

    functionrunMeFirstsetTimeout console.log 

    and the output would be in

    Script loadedMy script is initialized

    If you don’t use setTimeout, the order of logs will be sequential.

    functionrunMeFirstrunMeFirst console.log 

    and the output is,

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    Javascript Coding Interview Practice Sample Interview Questions And Solutions

    David Goggins is an ultramarathon runner, a public speaker, a retired navy SEAL, and the author of the book ‘Can’t Hurt Me: Master Your Mind and Defy the Odds‘. He’s one of my role models because of his physical strength and mental resilience.

    You might say: “Wait a second! We get it. This person is obviously the epitome of success. But he has non-technical skills. So why is he relevant to JavaScript coding interviews?”

    Well, if you’re ready, let’s explore this together.

    What Do Mean By Prototype Design Pattern

    JS Coding Interview Question: Build a Function that Tests to See if a ...

    The Prototype Pattern produces different objects, but instead of returning uninitialized objects, it produces objects that have values replicated from a template or sample object. Also known as the Properties pattern, the Prototype pattern is used to create prototypes.

    The introduction of business objects with parameters that match the database’s default settings is a good example of where the Prototype pattern comes in handy. The default settings for a newly generated business object are stored in the prototype object.

    The Prototype pattern is hardly used in traditional languages, however, it is used in the development of new objects and templates in JavaScript, which is a prototypal language.

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    How Do You Group And Nest Console Output

    The console.group can be used to group related log messages to be able to easily read the logs and use console.groupEndto close the group. Along with this, you can also nest groups which allows to output message in hierarchical manner.

    For example, if youre logging a users details:

    console.group console.log console.log // Nested Groupconsole.group console.log console.log console.log console.groupEnd 

    You can also use console.groupCollapsed instead of console.group if you want the groups to be collapsed by default.

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    Is Javascript A Compiled Or Interpreted Language

    JavaScript is an interpreted language, not a compiled language. An interpreter in the browser reads over the JavaScript code, interprets each line, and runs it. Nowadays modern browsers use a technology known as Just-In-Time compilation, which compiles JavaScript to executable bytecode just as it is about to run.

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    How To Remove All Line Breaks From A String

    The easiest approach is using regular expressions to detect and replace newlines in the string. In this case, we use replace function along with string to replace with, which in our case is an empty string.


    In the above expression, g and m are for global and multiline flags.

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    What Is The Distinction Between Client

    Javascript Coding Interview Questions – #18 | Javascript Interview Questions Answers Coding 2022

    Client-side JavaScript is made up of two parts, a fundamental language and predefined objects for performing JavaScript in a browser. JavaScript for the client is automatically included in the HTML pages. At runtime, the browser understands this script.

    Client-side JavaScript is similar to server-side JavaScript. It includes JavaScript that will execute on a server. Only after processing is the server-side JavaScript deployed.

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    Top 100 Javascript Interview Questions And Answers For 2022

    To build a JavaScript programming career, candidates need to crack the interview. They are asked for variousJavaScript interview questions and answers.

    Following is a list of JavaScript interview questions and answers, which are likely to be asked during the interview. Candidates are likely to be asked basic JavaScriptinterview questions to advance JS interviewquestions depending on their experience and various other factors.

    The below list covers all the JavaScriptquestions for freshers and JavaScriptinterviewquestions for professional-level candidates. This JS interviewquestions guide will help you crack the interview and help you get your dream job for JavaScript Programming.

    When Can You Have An Error That Says Undefined Value On The Screen

    Well, if it appears, it simply means either the variable the user is considering doesnt exist in the code. It is also possible that the property is not present. In addition to this, the error can also be due to the fact that the variable hasnt been assigned any value. Users need to make sure of these three steps before they proceed with anything. If this error is ignored, it can sometimes affect the entire code.

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    What Do You Understand By Hoisting In Javascript

    Hoisting is the default behavior of JavaScript where all the variable and function declarations are moved on top. In simple words, we can say that Hoisting is a process in which, irrespective of where the variables and functions are declared, they are moved on top of the scope. The scope can be both local and global.

    Example 1:


    Difference Between Async/await And Generators Usage To Achieve The Same Functionality

    Coding Interview Question: Build a Function that Selects a Random ...
    • Generator functions are run by their generator yield by yield which means one output at a time, whereas Async-await functions are executed sequentially one after another.
    • Async/await provides a certain use case for Generators easier to execute.
    • The output result of the Generator function is always value: X, done: Boolean, but the return value of the Async function is always an assurance or throws an error.

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    Javascript Interview Prep Cheatsheet Ace Your Coding Interviews With These Concepts

    I’ve carefully gone through over 50 resources, I’ve been through 10 JavaScript interviews, and I’ve landed a job at a unicorn startup.

    And throughout this entire process, I started to see a pattern in the most frequently asked JS interview questions.

    In this article, I have tried to list the concepts which will cover 80% of any good JS interview.

    So, if you are prepping for your next JS interview this is the perfect cheatsheet for you to review and solidify your skills. Go through this and you’ll be ready to rock.

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