Accenture JavaScript Most Frequently Asked Latest Interview Questions Answers
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'];
AJAX requests should use an HTTP GET request where the data does not change for a given URL requested.
An HTTP POST should be used when state is updated on the server. This is highly recommended for a consistent web application architecture.
What are the limitations of Ajax?
An Ajax Web Application tends to confuse end users if the network bandwidth is slow and there is no full postback running.
What is AJAX Framework?
ASP.NET AJAX is a free framework to implement Ajax in asp.net web applications. It is used to quickly creating efficient and interactive Web applications that work across all browsers.
How can we cancel the XMLHttpRequest in AJAX?
Abort() method can be called to cancel the XMLHttpRequest in Ajax.
Is AJAX code cross browser compatible?
No, it is supporting cross browser compatible. If the browsers supports native XMLHttpRequest JavaScript object, then this can be used.
What is the name of object used for AJAX request?
XmlHttpRequest object is used for Ajax requests.
What is prerequisite for Update Panel in Ajax?
Script Manager is pre-requisite to use Update Panel controls.
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.)
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| Accenture JavaScript Most Frequently Asked Latest Interview Questions Answers |
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 advantages of jQuery?
Following are the advantages of jQuery:
Just a JavaScript enhancement
Coding is simple, clear, reusable
Removal of writing more complex conditions and loops
Whether C# code behind can be called from jQuery?
Yes, we can call C# code behind from jQuery.
What is the use of jQuery.data() method?
jQuery data method is used to associate data with DOM nodes and JavaScript objects. This method will make a code very concise and neat.
What is the difference between onload() and document.ready()?
In a page, we can have only one onload function but we can have more than one document.ready function. Document.ready function is called when DOM is loaded but onload function is called when DOM and images are loaded on the page.
What is the use of jQuery each function?
jQuery each function is used to loop through each and every element of the target jQuery object. It is also useful for multi element DOM, looping arrays and object properties.
How method can be called inside code behind using jQuery?
$.ajax can be called and by declaring WebMethod inside code behind using jQuery.
Which is the fastest selector in jQuery?
ID and Element are the fastest selectors in jQuery.
What is the slowest selector in jQuery?
Class selectors are the slowest selectors in jQuery.
Which request is better, Get or Post?Following are the advantages of jQuery:
Just a JavaScript enhancement
Coding is simple, clear, reusable
Removal of writing more complex conditions and loops
Whether C# code behind can be called from jQuery?
Yes, we can call C# code behind from jQuery.
What is the use of jQuery.data() method?
jQuery data method is used to associate data with DOM nodes and JavaScript objects. This method will make a code very concise and neat.
What is the difference between onload() and document.ready()?
In a page, we can have only one onload function but we can have more than one document.ready function. Document.ready function is called when DOM is loaded but onload function is called when DOM and images are loaded on the page.
What is the use of jQuery each function?
jQuery each function is used to loop through each and every element of the target jQuery object. It is also useful for multi element DOM, looping arrays and object properties.
How method can be called inside code behind using jQuery?
$.ajax can be called and by declaring WebMethod inside code behind using jQuery.
Which is the fastest selector in jQuery?
ID and Element are the fastest selectors in jQuery.
What is the slowest selector in jQuery?
Class selectors are the slowest selectors in jQuery.
AJAX requests should use an HTTP GET request where the data does not change for a given URL requested.
An HTTP POST should be used when state is updated on the server. This is highly recommended for a consistent web application architecture.
What are the limitations of Ajax?
An Ajax Web Application tends to confuse end users if the network bandwidth is slow and there is no full postback running.
What is AJAX Framework?
ASP.NET AJAX is a free framework to implement Ajax in asp.net web applications. It is used to quickly creating efficient and interactive Web applications that work across all browsers.
How can we cancel the XMLHttpRequest in AJAX?
Abort() method can be called to cancel the XMLHttpRequest in Ajax.
Is AJAX code cross browser compatible?
No, it is supporting cross browser compatible. If the browsers supports native XMLHttpRequest JavaScript object, then this can be used.
What is the name of object used for AJAX request?
XmlHttpRequest object is used for Ajax requests.
What is prerequisite for Update Panel in Ajax?
Script Manager is pre-requisite to use Update Panel controls.
What is a Typed Language?
Typed Language is in which the values are associated with values and not with variables. It is of two types:
Dynamically: in this, the variable can hold multiple types; like in JS a variable can take number, chars.
Statically: in this, the variable can hold only one type, like in Java a variable declared of string can take only set of characters and nothing else.
NOTE: Typescript is a superset of JS which is of typed language.
What does a typeof operator do?
The operator typeof gives the type of a variable/data available in it. The typeof operator can be used on Reference data types also.
Name some of the ways in which Type Conversion is possible.
Type Conversion is to convert from one data type to another data type.
(i) Number to String Conversion.
toString: Other data type to String.
val = (5).toString(); converts integer to string.
val = (true).toString(); converts boolean to string.
Convert from Number/Boolean/Date to String.
Number to String: String(9) converts num to string
Boolean to String: String(true) converts bool to str
Date to String: String(new Date()) date to string
Array to String: String([2,2,2]) Array to string.
(ii) String to Number Conversion.
parseInt: String to Int only (no decimals)
val = parseInt('11'); outputs 100 as number
val = parseFloat('22.22') outputs 22.22 as float
Convert from String/Boolean to Number/Date.
String to Number: Number('9') converts str - num
(9).toFixed(4) gives 9.0000 as the output
Boolean to Number: Number(true) converts to no.
Null to Number: Number(null) converts to no. (0)
Chars to Number: Number('ss') give NaN.
What is the difference between Local Storage and Session Storage?
Local Storage will stay until it is manually cleared through settings or program.
Session Storage will leave when the browser is closed.
What is the difference between the keywords var and let?
The keyword var is from the beginning of Javascript; whereas, let is introduced in ES2015/ES6. The keyword let has a block scope; whereas, the keyword var has a functional scope.
What is the difference between the operators '==' and '==='?
The operator '==' compares the value; whereas, the operator '===' compares both value and type.
Typed Language is in which the values are associated with values and not with variables. It is of two types:
Dynamically: in this, the variable can hold multiple types; like in JS a variable can take number, chars.
Statically: in this, the variable can hold only one type, like in Java a variable declared of string can take only set of characters and nothing else.
NOTE: Typescript is a superset of JS which is of typed language.
What does a typeof operator do?
The operator typeof gives the type of a variable/data available in it. The typeof operator can be used on Reference data types also.
Name some of the ways in which Type Conversion is possible.
Type Conversion is to convert from one data type to another data type.
(i) Number to String Conversion.
toString: Other data type to String.
val = (5).toString(); converts integer to string.
val = (true).toString(); converts boolean to string.
Convert from Number/Boolean/Date to String.
Number to String: String(9) converts num to string
Boolean to String: String(true) converts bool to str
Date to String: String(new Date()) date to string
Array to String: String([2,2,2]) Array to string.
(ii) String to Number Conversion.
parseInt: String to Int only (no decimals)
val = parseInt('11'); outputs 100 as number
val = parseFloat('22.22') outputs 22.22 as float
Convert from String/Boolean to Number/Date.
String to Number: Number('9') converts str - num
(9).toFixed(4) gives 9.0000 as the output
Boolean to Number: Number(true) converts to no.
Null to Number: Number(null) converts to no. (0)
Chars to Number: Number('ss') give NaN.
What is the difference between Local Storage and Session Storage?
Local Storage will stay until it is manually cleared through settings or program.
Session Storage will leave when the browser is closed.
What is the difference between the keywords var and let?
The keyword var is from the beginning of Javascript; whereas, let is introduced in ES2015/ES6. The keyword let has a block scope; whereas, the keyword var has a functional scope.
What is the difference between the operators '==' and '==='?
The operator '==' compares the value; whereas, the operator '===' compares both value and type.
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