Today #Day113 of #365DaysOfCode, Learning Top JavaScript Interview Questions.

Intermediate JavaScript Interview Questions,

21. What are closures in JavaScript?

Closures provide a better and more concise way of writing JavaScript code for developers and programmers.

Closer is created whenever a variable that is defined outside the current scope is accessed within the current scope.

function hello(name){
var message = "hello" + name;
return function hello () {
console.log(message );
};
}
//generate closure
var helloWorld = hello("world");
//use closure
helloWorld();

22. What are arrow functions in JavaScript?

Arrow functions are a short way of writing functions in JavaScript.

cpnst helloWorld = ()=> {
console.log("hello world");
}

23. What are the different ways an HTML element can be accessed in JavaScript code?

Accessor	description
getElementByClass('classname')	Gets all the HTML elements that have the specified classmate.
getElementById('idname')	get an HTML element by its ID name
getElementsbyTagName('tagname')	gets all the HTML elements that have the specified tag name
querySelector()	Takes CSS style selector and returns the first selected HTML element

24. What are the ways of defining a variable?

There are 3 ways of defining a variable in JavaScript:

var - this is used to declare a variable and the value can be changed at a later time within the JavaScript code. var abc = 'Hello';

const - we can also use this to declare/ define if variable but the value is constant throughout the JavaScript program and cannot be modified. const abc = 'Hello';

let - this mostly implies that the values can be changed at a later time within the JavaScript code. let abc = 'Hello';

25. what are imports and exports in JavaScript?

Imports and exports help in writing modular court for our JavaScript applications.

With the help of imports and exports split a JavaScript code into multiple files in a project

to make JavaScript highly reusable and modular us imports and export commands in JavaScript programs.

The below JavaScript code snippet file exports to functions that calculate the square and diagonal of the input respectively.

export const sqrt = Math.sqrt;
export function square(x) {
return x * x;
}
export function diag(x,y){
return sqrt (square(x) + square(y));
}

the below code we import those functions and pass input to those functions to calculate square and diagonal,

import {square,diag} from "calc;
console.log(square(4));
console.log(diag(4,3));

26. What is the difference between a document and a window in JavaScript?

Windows are top-level object and document object falls under this.

27. What are some of the JavaScript frameworks and their users?

JavaScript has a collection of many frameworks that aim towards fulfilling the different aspects of web application development process.

Some of the prominent frameworks are:

react- front end development of a web application.

Angular- front end development of web application

Node JS- backend or server-side development of a web application.

28. What is the difference between undefined and undeclared in JavaScript?

29. What is the difference between undefined and null in JavaScript?

30. What is the difference between session storage and local storage in JavaScript?

Advanced JavaScript Interview Questions

31. How do you empty an array in JavaScript?

There are few ways in which we can empty an array in JavaScript.

By assigning array length 20.

var arr = [1,2,3,4];
arr.length = 0;

by assigning an empty array,

var arr = [1,2,3,4]; 
arr = [];

by popping the elements of the array,

var arr = [1,2,3,4]; 
while(arr.length>0){
arr.pop();
}

by using the splice array function,

var arr = [1,2,3,4]; 
 arr.splice(0,are.length);

32. What is the difference between event capturing an event bubbling?

33. What is the strict mode in JavaScript?

Strict mode in JavaScript introduces mode stringent error- checking in a JavaScript code.

While in strict mode all variables have to be declared explicitly, values cannot be assigned to a read-only property etc.

We can enable strict mode by adding use strict at the beginning of a JavaScript code or within a certain segment of code.

'use strict';
let a = 10, 
b = 20, 
c= a + b;

34. What would be the output of the below JavaScript code?

var a =10;
if (function abc () {}){
a+= typeof abc;
}
console.log(a);

the output of this JavaScript JavaScript code will be 10 undefined.

Then if condition statement in the code evaluates using eval,

hence, eval(function abc () {}) will return function abc () {},

inside the if statement executing type of abc returns undefined because the if statement code executes at runtime while the statement inside the if condition is being evaluated.

35. Can you write a JavaScript code for adding a new elements in a dynamic manner?

function addNode(){
    var newP = document.createElement("p");
    var textNode = document.createTextNode("This is a new text node")
    newP.appendChild(textNode);
    document.getElementById("firstP").appendChild(newP)
}

36. What is the difference between call and apply?

37. What would be the output of the below JavaScript code?

var Student = {
    college: 'abc',
};
var stud1 = Object.create(Student);
console.log(Student);
delete stud1.college
console.log(stud1);

console.log(stud1.college);

this is basically a simple example of object-oriented programming.

Therefore the output will be 'abc' as we are accessing the property of the student object.

38. What would be the output of the below JavaScript code?

var Bar = Function Foo(){
    return 11;
};
typeof Foo();

The output would be a reference error since function definition can only have a single reference variable as its name.

39. How do you remove duplicates from a JavaScript array?

There are 2 ways in which we can remove duplicates from a JavaScript array:

By using filter method - in order to call the filter() method, 3 arguments are required. These are namely array, current element, and index of the current element.

By using the for loop - and MTR is used for storing all the repeating elements.

40. Can you draw a simple JavaScript Dom (document object model)?

Here simple diagram of document object model of a web page,

Conclusion

I learned and practiced Top JavaScript Interview Questions.

Code

1. code

   

Source: Simplilearn [Link]

Author: Dheeraj.y

Connect with me:

• My Twitter

• My LinkedIn

• My GitHub

• My Hashnode