JavaScript - Marathon Interview Questions Series 2024

Related Questions :-

1. What is undefined in JavaScript?

2. What will be the output of undefined==null and undefined===null? Why?

3. Can you explicitly assign ‘undefined’ to a variable?

   let i=undefined; [show example]

Related Questions :-

1. What is hoisting in JavaScript?

2. How does block scope work?

3. What is the scope of a variable?

Related Questions :-

1. Should you terminate all lines by a “;”?

2. function test(){

   return

   {

   a:5

   }

   }

   const obj=test();

   console.log(obj);

   Why this code is returning undefined in spite of function returning a valid object literal?

3. Can ‘use strict’ statement or the strict mode change the behavior of ASI?

Related Questions :-

1. Can we use arguments object in arrow function?

2. Which is the best way to create new arrays with assignment?

3. How can you handle the “n” number of parameters passed to a function ? or create a function which can take any number of parameters and returns sum or max or any other such calculative values.

4. Can the rest operator be placed anywhere in the function parameter list? Or

   function test(...a,b){

   //statements

   }

   Is this piece of code valid? Give the reason.

   
   

Related Questions :-

1. How will you put a validation for positive or negative Infinity?

2. What will be the output of this code?

   Code:

   console.log(1/0);

Related Questions :-

1. What will be the output of the below statement?

   console.log(NaN==NaN);

2. What is the difference between isNaN() and isFinite() method?

Related Questions :-

1. How can you access private variable or function outside the scope?

2. Explain the advantage of closure?

Related Questions :-

1. What is function currying?

2. const multiplication=a=>b=>c=>return a*b*c

   What will this statement do? Explain in detail.

3. Explain practical usage of function currying.

Relative Questions :

1) What is the purpose of the iterator ?

2) How do you create an iterator ?

3) Explain a practical use of an iterator ?

Related Questions :-

1. What are generator functions? Explain the syntax.

2. Which is the right syntax function* (){} or function *(){}?

3. Explain all methods of generator objects.

4. Explain the use of “yield*”.

5. Can you prevent return() from terminating the generator?

Related Questions :-

1. How does Garbage Collection work in JavaScript?

2. Explain “Mark-and-Sweep” algorithm’s pattern.

3. Which situation can create a memory leak?

Related Questions :-

1. When do you need try...catch?

2. How can you generate an error?

3. Can you generate SyntaxError or ReferenceError kind of errors?

4. What is the purpose of the finally block?

5. How can you refer to the name or description of error?

6. Can we have finally without a catch block as well?

Related Questions :-

1. What is the difference between for...in and for...of?

2. What will be the output of the below code?

   =>

   let arr = ["ES5","ES6","ES7","ES8"];

   arr.forEach(function(element,index){

   console.log(element,index);

   if (index==2){

   break;

   }

   })

3. What will be the output of below statements?

   =>

   let arr=[7,9,0];

   console.log(arr[arr.length]);

Related Questions :-

1. What is the difference between push() and unshift() method?

2. What is the difference between pop() and shift()?

3. How can you insert an element at a given position?

4. How can you remove a specific element?

5. What does splice() return?

6. If there is no element removed then what will splice() method return?

Related Questions :-

1. What is the difference between find() and filter() method?

2. If there is no value to return, what will findIndex() return?

3. What is the difference between indexOf() and includes() method?

4. How will you search multiple values in an array?

5. What will be the output of this code?

   let arr=["One","Two","Three","Four","Five"];

   console.log(arr.lastIndexOf("Abcd"));

Related Questions :-

1. Find the length of each element in a new array.

2. Find the square root of every element and store it in a new array.

3. There is an array called products as shown here

   let products=[

   {pCode:1,pName:"Apple"},

   {pCode:2,pName:"Banana"},

   {pCode:3,pName:"Grapes"},

   {pCode:4,pName:"Oranges"}

   ]

   Get all product names (i.e pNames) in a new array

Related Questions :-

1. How will you flatten an array i.e e.g converting a 2 dimensional array into single dimension?

2. Get sum of a key field of an object literal & Then find total salary of employees

   const employees=[

   {eNo:1001,salary:3000},

   {eNo:1002,salary:2200},

   {eNo:1003,salary:3400},

   {eNo:1004,salary:6000}

   ]

3. Find avg value of all elements of an array?

4. Find the sum or product of all elements?

5. What is the difference between reduce() and reduceRight()?

Related Questions :-

1. What will be the output in case an array has “undefined” while sorting the values?

2. How will sort an object literal?

3. How will you sort a numeric array?

4. Sort all values of the array in descending order.

Related Questions :

1. What is the destructuring assignment?

2. Swap values using destructuring.

3. What will be the output of this code?

   => let [a,b,c] = [5,,7];

        console.log(a,b,c);

4. How will you set a default value while destructuring an array?

Related Questions :-

1. Explain various ways to declare a string variable.

2. How will you deal with unicode characters?

3. Show the syntax to display long unicode characters.

Related Questions :-

1. What is a template literal?

2. How will you display a value or an expression inside template string?

3. What is the advantage of using template string?

Related Questions :-

1. Explain the indexOf() and lastIndexOf() method with syntax.

2. What is the difference between search() and indexOf() method?

3. What will be the output of the below given code? Explain with reason.

   let str="This is a test";

   console.log(str.indexOf("is",5));

   console.log(str.lastIndexOf("is",1));

Related Questions :-

1. Create a program which check whether a character is vowel or consonant

Related Questions :-

1. Explain different ways of creating date/time object

2. What will be the output of the below code

   => const dt = new Date(2020,08,23);

         console.log(dt);

3. Explain various formats of ISO standard followed by JavaScript ?

Related Questions :-

1. Get Character month.

2. Find the date before 50 days of the given date.

3. What will be the output if you add 35 as date in Date() constructor.

Related Questions :-

1. Calculate the date difference in days.

2. How can you change hours or minutes in time ?

Related Questions :-

1. Can you have dynamic keys with object literal?

2. How can you add read-only properties to an object?

3. What is property value short hand with object literal?

4. What will be the output of this code

   let obj={a:'First'};

   let obj1 = obj;

   obj1.a="Second";

   console.log(obj.a);

   Explain the reason why?

5. How can we create a clone or separate copy of an object literal?

Related Questions :-

1. What will be the output of this code if you run in the browser and why?
   function test(){

   console.log(this);

   }

   test();

2. What is the context of “this” inside arrow function? Or what will be the output of this code
   let obj={

   
   

   test:()=>{

   console.log(this);

   }

   }

   obj.test();

Related Questions :-

1. What is the difference between call, apply and bind()?

2. What will be the output of this code? Or can you assign value to “this” object with assignment operator i.e. “=”?

   const obj={

   a:6

   }

   function test(){

   this=obj;

   }

   test();

Related Questions :-

1. How can you create a class?

2. When does constructor() called?

3. Can we have dynamic property or method names in a class?

4. What is a class expression?

5. What are static members in a class? What is the purpose of defining them as static?

6. How can you call another static method from a class?

Related Questions :-

1. How can you inherit a class?

2. What is subclassing?

3. What is the purpose of super keyword?

4. How will you override a method?

5. How can you extend a built-in class?

Related Questions :-

1. Explain a practical scenario of object literal destructuring ?

2. Explain the output of this code

   const { a=90, b } = { };

   console.log(a,b);

Related Questions :-

1. What is a getter or setter method?

Related Questions:-

1. What are the advantages of using Map over objects?

2. How will you iterate through Map ?

3. Can you assign key/values with this syntax ? Explain the reason for the answer - map[‘key’]=value

4. How can you convert simple objects to Map?

5. How can you convert a Map into simple objects?

6. How will you remove an item or all items from Map?

   
   

Related Questions:-

1. What is the difference between Map and Set ?

2. How will you remove specific values from Set ?

3. What will entries() method with Set will return ?

Related Questions :-

1. Explain difference Between Map and WeakMap.

2. Explain difference Between Set and WeakSet.

Related Questions :-

1. What is DOM or DOM API?

2. What is a DOM Tree?

3. What do you mean by DOM Manipulation?

Related Questions :-

1. What is the difference between window and document?

2. What is DOM [Document Object Model] or DOM API?

3. What is BOM [Browser Object Model]?

4. Explain the difference between DOM and BOM?

5. Which is the global object in browser?

6. How will we check the width and height of window?

7. How will you get hostname or value typed in address bar?

Related Questions :-

1. Explain the difference between setTimeout() and setInterval()?

2. Why can’t we write document.setTimeout() or document.setInterval()?

3. How can you stop a timer ?

4. How will you create a digital clock ?

Related Questions :-

1. Which is the default propagation path?

2. How can you stop the event propagation?

3. How can you change the default propagation path?

4. How can you get the reference of element on which event is fired?

5. Practical question :- What will be the output of code & why?

Related Questions :-

1. How event bubbling or capturing is useful in the practical programming world?

2. Which property can be used to check the element type on which the event is triggered?

3. How can you get value of the element which raised the event?

Related Questions :-

1. What is a node in DOM tree? Explain different types of nodes?

2. How can you access next same level element for a given node element?

3. What is the difference between childeNodes and children property?

4. How can you check whether an element has child nodes or not?

5. What is the purpose of DOM navigation?

6. What will be the output of below given statement? - element.lastChild.nextSibling

Related Questions :-

1. Can you use document.getElementById() & element.getElementById() ?

2. What does the getElementsByTagName() return ?

3. What is the difference between getElementsByClassName() & getElementsByName() ?

Related Questions :-

1. Explain the difference between querySelector() & querySelectorAll().

2. How can you search elements using pseudo classes?

3. Between getElementBy methods and querySelector methods which is better to use?

Related Questions :-

1. Explain various ways to configure an event with HTML elements.

2. Explain syntax of addEventListener() method.

3. What is an event object ?

Related Questions :-

1. How will you disable right click on an element?

2. How can you check whether a special key is pressed or not while an event is generated?

3. How do you check mouse button value while an event is generated?

4. For ctrl key and cmd on mac - how will you right the condition to check the key press.

Related Questions :-

1. Explain the difference between clientX/Y and pageX/Y.

2. Explain the difference between clientX/Y and screenX/Y.

Related Questions :-

1. How can you check if control and Z is pressed or not?

2. What does event.code return ?

3. Explain the difference between event.code and event.key ?

Related Questions :-

1. What is the difference between onblur and onchange event?

2. How will you handle events of checkbox and radio buttons?

3. Differentiate onkeypress/onkeyup and oninput event.

4. Which event you prefer with select [i.e. drop down list]?

5. How will you get the text value of selected item from a select element i.e. a drop down list?

Related Questions :-

1. Explain about cut,copy and paste events

2. How can you stop an event of cut, copy or paste for an element ?

Related Questions :-

1. Explain what is a web component and how can you create it?

Related Questions :-
1. What is shadow DOM? Explain the need for it.

2. How do you add a component to a shadow DOM?

Related Questions :-
1. What is the purpose of the <template> tag?

Related Questions :-
1. What is the observerdAttributes() method’s functionality?

2. When will the attributeChangedCallback() method be invoked?

3. How can you improve rendering with the help of attributeChangedCallback()?

Related Questions :-
1. Explain the purpose of disconnectedCallback() life cycle method.

Related Questions :-
1. What is light DOM?

2. How can you manage or display the content placed inside the custom HTML element?

Related Questions :-

1. What is an Asynchronous process?

2. What is the meaning of callback hell or pyramid of doom?

Related Questions :-

1. How will you configure a process which should be executed at the end of promise resolve or reject ?

2. What is chaining the promise? Explain the syntax.

3. What will be the output of the given code?

   const pr = new Promise((resolve,reject)=>{

   resolve("Over");

   setTimeout(()=>{

   resolve("Again");

   },2000)

   })

   
   

   pr.then((msg)=>{

   console.log(msg);

   return pr;

   }).then((msg)=>{

   console.log(msg);

   })

4. What is the status of promise by default?

5. What will be the status of promise when resolved or rejected?

Related Questions :-

1. What will be the output if the iterable is not a promise inside all() method arguments,e.g as shown below where “p2” is not a promise?

   const p1 = new Promise((resolve,reject)=>{

   setTimeout(()=>{

   resolve("Promise1");

   },2000)

   })

   const p2 = "Normal string";

   const p3 = new Promise((resolve,reject)=>{

   setTimeout(()=>{

   resolve("Promise3");

   },2000)

   })

   
   

   Promise.all([p1, p2,p3]).then((prMsgs) => {

   console.log(prMsgs);

   }).catch((err)=>{

   console.log(err);

   })

2. How will you handle rejected multiple promises in the most efficient way?

3. Explain the purpose of Promise.race() method.

4. What will be the output of empty iterable if given as a parameter inside the race() method as shown in this code?

   const obj = Promise.race([]);

   console.log(obj);

   
   

   setTimeout(()=>{

   console.log(obj);

   },2000);

Related Questions :-

1. Can you write await without async?

2. Do you need to return a promise from an async function?

3. Can you have an async IIFE?

4. Which is the best way to handle errors with await?

5. Explain the syntax of Promise.all() with async/await?

Related Questions :-

1. What is AJAX?

2. How will you set a timeout with an XHR request?

3. How can you set the data format for response?

4. Explain “readyState” property of XHR.

5. Explain the “onreadystatechange” event.

6. How can you force the XHR request to stop the execution?

7. When is the “load” method called?

8. How will you set HTTP headers? Explain the sequence.

9. Explain different ways of getting response header values?

Related Questions :-

1. Explain the fetch API functionality.

2. How will you make a DELETE request with fetch API?

Related Questions :-

1. What is Symbol.asyncIterator?

2. Can we use spread operator with async iterator e.g. [...obj]?

3. How will you handle the async iterator using generator function syntax?

Related Questions :-

1. What is a module ?

2. Can you import any module inside the script tag ?

3. How will you run the import and export statements on a local machine ?

Related Questions :-

1. What is a named export and import ?

2. Can you avoid {} while importing a named module ?

3. How can you import all named modules from a file ?

4. Is it a good practice to import all modules together ?

5. Do the modules hoist ?

6. Do you need the same name while importing a named module or you can change ?

Related Questions :-

1. What is default export/import & the difference between named & default export/import ?

2. Explain various ways of implementing default export/import ?