October 13, 2018

Sreekanth B

Intel JavaScript Most Frequently Asked Latest Interview Questions Answers

What is the difference between the operators '=='  and '==='?

The operator '==' compares the value; whereas, the operator '===' compares both value and type.

What is the difference between null and undefined?

When used the typeof operator on null; i.e., typeof(null), the value is an object. Whereas, when used the typeof operator on undefined; i.e., typeof(undefined), the value would be undefined.

Are Javascript and JScript the same?

No, Javascript was provided by Netscape; whereas, JScript was provided by Microsoft.

Are Typescript and Javascript the same?

Typescript is not the next version of Javascript but is developed by Microsoft and can be taken as a superset to Javascript; the code written in Typescript is later compiled into Javascript. Typescript adds new features like Interfaces, Generics, etc.

Name some of the Javascript frameworks.

There are many Javascript Frameworks available today, but the most commonly used frameworks are:

(i) Angular (ii) React (iii) Vue
Intel JavaScript Most Frequently Asked Latest Interview Questions Answers
Intel JavaScript Most Frequently Asked Latest Interview Questions Answers

Explain the typeof operator.

The operator typeof is an example of Unary Operators, which is used by placing it before its operand; which can be of any type.

What are anonymous functions in Javascript?

An anonymous function allows a developer to create a function that has no name. In other words, anonymous functions can be used to store a bit of functionality in a variable and pass that piece of functionality around.

What is the difference between an Anonymous Function and a named function?

Anonymous functions exist only after they are called; whereas, Named functions to exist even if not called.

What are self Executing Functions?

These functions are executed right after its definition.  Also called as Immediately Invoked Function Expressions (IIFE's). Syntax:
(function(){
    console.log('in iffe');
})()

What is a function callback?

The callback function is a mechanism to send one function to another function as an argument; i.e., passing func as an argument to another function.

What happens when the recursion calling is applied on two functions?

The calling of recursion is possible in two functions, but the call comes to an end after some time.

Explain the term closure.

The inner functions can be called as closure when it has access to the outer function's variables.

Explain the terms synchronous and asynchronous code.

The synchronous code is something that should be finished before anything else can happen, or in other words, the synchronous code is blocking. And the Asynchronous code is something in which actions can happen and is not dependent on other actions- in other words, it is non-blocking.

Consider the following code. What will the output be, and why?

(function () {
    try {
        throw new Error();
    } catch (x) {
        var x = 1, y = 2;
        console.log(x);
    }
    console.log(x);
    console.log(y);
})();

1
undefined
2
var statements are hoisted (without their value initialization) to the top of the global or function scope it belongs to, even when it’s inside a with or catch block. However, the error’s identifier is only visible inside the catch block. It is equivalent to:

(function () {
    var x, y; // outer and hoisted
    try {
        throw new Error();
    } catch (x /* inner */) {
        x = 1; // inner x, not the outer one
        y = 2; // there is only one y, which is in the outer scope
        console.log(x /* inner */);
    }
    console.log(x);
    console.log(y);
})();

What will be the output of this code?

var x = 21;
var girl = function () {
    console.log(x);
    var x = 20;
};
girl ();

Neither 21, nor 20, the result is undefined

It’s because JavaScript initialization is not hoisted.

(Why doesn’t it show the global value of 21? The reason is that when the function is executed, it checks that there’s a local x variable present but doesn’t yet declare it, so it won’t look for global one.)

How do you clone an object?

var obj = {a: 1 ,b: 2}
var objclone = Object.assign({},obj);
Now the value of objclone is {a: 1 ,b: 2} but points to a different object than obj.

Note the potential pitfall, though: Object.clone() will just do a shallow copy, not a deep copy. This means that nested objects aren’t copied. They still refer to the same nested objects as the original:

let obj = {
    a: 1,
    b: 2,
    c: {
        age: 30
    }
};

var objclone = Object.assign({},obj);
console.log('objclone: ', objclone);

obj.c.age = 45;
console.log('After Change - obj: ', obj);           // 45 - This also changes
console.log('After Change - objclone: ', objclone); // 45

for (let i = 0; i < 5; i++) {
  setTimeout(function() { console.log(i); }, i * 1000 );
}
What will this code print?

It will print 0 1 2 3 4, because we use let instead of var here. The variable i is only seen in the for loop’s block scope.

What do the following lines output, and why?

console.log(1 < 2 < 3);
console.log(3 > 2 > 1);

The first statement returns true which is as expected.

The second returns false because of how the engine works regarding operator associativity for < and >. It compares left to right, so 3 > 2 > 1 JavaScript translates to true > 1. true has value 1, so it then compares 1 > 1, which is false.

How do you add an element at the begining of an array? How do you add one at the end?

var myArray = ['a', 'b', 'c', 'd'];
myArray.push('end');
myArray.unshift('start');
console.log(myArray); // ["start", "a", "b", "c", "d", "end"]
With ES6, one can use the spread operator:

myArray = ['start', ...myArray];
myArray = [...myArray, 'end'];
Or, in short:

myArray = ['start', ...myArray, 'end'];

What are the disadvantages of Ajax?

Following are the disadvantages of Ajax:

AJAX is dependent on Javascript. If there is some Javascript problem with the browser or in the OS, Ajax will not support
Ajax can be problematic in Search engines as it uses Javascript for most of its parts.
Source code written in AJAX is easily human readable. There will be some security issues in Ajax.
 Debugging is difficult
 Increases size of the requests
 Slow and unreliable network connection.
Problem with browser back button when using AJAX enabled pages.

What is update panel?

Update panel  is a server control used to update the specified portion of a web page. Script Manager needs to be used whenever update panel is used. Using update panel, user cannot handle outside controls.

Which are the two methods used for cross domain Ajax calls?

There are two methods used to transfer data between the two more more security domains:

CORS – Cross Origin Resource Sharing and it works with the HTTP web browsers
JSONP – JSON with Padding which works with the HTTP GET and on legacy browsers

What are all the technologies used by Ajax?

AJAX uses following technologies:

JavaScript
XMLHttpRequest
Document Object Model (DOM)
Extensible HTML (XHTML)
Cascading Style Sheets (CSS)

What are all the features of Ajax?

Following are the features of Ajax and they are as follows:

Live data binding
Client-side template rendering
Declarative instantiation of client components
Observer pattern on JavaScript objects and arrays
Invoking ADO.NET data services and data contexts
DataView control

What are Ajax applications?

Browser based applications and platform independent applications are used by Ajax.

How many types of triggers are present in update panel?

There are two types of triggers used in update panel:

PostBackTrigger – This works as full postback and it cannot work asynchronously
AsyncPostBackTrigger – Partial post back asynchronously

What are all the controls of Ajax?

Following are the controls of Ajax:

ScriptManager
ScriptManagerProxy
UpdatePanel
UpdateProgress
Timer.

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