Deloitte JavaScript Most Frequently Asked Latest Interview Questions Answers
How can AJAX applications be debugged?
Two tools are used for debugging:
Fiddler for IE
Firebug for Mozilla.
What is Script Manager?
Script Manager helps manage the client side script of AJAX. Script Manager acts as a mediator as AJAX depends on JavaScript. Every page that uses AJAX has a Script Manager to enable AJAX libraries.
How Ajax objects can be created?
Following syntax can be used to create Ajax objects:
Var sample = New ajaxObject(‘path of the page’)
What are all the different data types that JSON supports?
JSON supports following data types:
String
Number
Boolean
Array
Object
Null
What are the goals of Ajax?
The basic goals of ASP.NET Ajax are:
Reduced web server hits
Reduced Network load
Interactive user interface
Platform and architecture neutrality
Support for both synchronous and asynchronous communication
Provide a server- and client-side framework
What is the difference between proxied and proxyless calls in AJAX?
Proxied calls are made through stub objects which can be called from PHP classes on the JavaScript side in AJAX.
Proxyless calls are made using utility JavaScript functions like HTML_AJAX.replace() and HTML_AJAX.append() in AJAX.
What are the protocols used by Ajax?
HTTP’s GET or POST
XMLHttpRequest for placing a request with the web server
Uses JSON to communicate between the client and server
UED or URL encoded data
What are all the security issues of Ajax?
Security issues that can be encountered
When Ajax calls are sent through plain text and it may lead to know the database details
Inserting scripts can also be possible and attackers can easily penetrate into the system
How can we handle concurrent requests?
Javascript functions should be written to handle concurrent requests and call back function can be passed as a parameter. Those parameters are passed to AjaxInteraction(URL, callback) object.
How can AJAX applications be debugged?
Two tools are used for debugging:
Fiddler for IE
Firebug for Mozilla.
What is Script Manager?
Script Manager helps manage the client side script of AJAX. Script Manager acts as a mediator as AJAX depends on JavaScript. Every page that uses AJAX has a Script Manager to enable AJAX libraries.
How Ajax objects can be created?
Following syntax can be used to create Ajax objects:
Var sample = New ajaxObject(‘path of the page’)
 |
| Deloitte JavaScript Most Frequently Asked Latest Interview Questions Answers |
What are all the different data types that JSON supports?
JSON supports following data types:
String
Number
Boolean
Array
Object
Null
What are the goals of Ajax?
The basic goals of ASP.NET Ajax are:
Reduced web server hits
Reduced Network load
Interactive user interface
Platform and architecture neutrality
Support for both synchronous and asynchronous communication
Provide a server- and client-side framework
What is the difference between proxied and proxyless calls in AJAX?
Proxied calls are made through stub objects which can be called from PHP classes on the JavaScript side in AJAX.
Proxyless calls are made using utility JavaScript functions like HTML_AJAX.replace() and HTML_AJAX.append() in AJAX.
What are the protocols used by Ajax?
HTTP’s GET or POST
XMLHttpRequest for placing a request with the web server
Uses JSON to communicate between the client and server
UED or URL encoded data
What are all the security issues of Ajax?
Security issues that can be encountered
When Ajax calls are sent through plain text and it may lead to know the database details
Inserting scripts can also be possible and attackers can easily penetrate into the system
How can we handle concurrent requests?
Javascript functions should be written to handle concurrent requests and call back function can be passed as a parameter. Those parameters are passed to AjaxInteraction(URL, callback) object.
What is the data type of variables of in JavaScript?
All variables in the JavaScript are object data types.
What is the difference between an alert box and a confirmation box?
An alert box displays only one button which is the OK button.
But a Confirmation box displays two buttons namely OK and cancel.
What are escape characters?
Escape characters (Backslash) is used when working with special characters like single quotes, double quotes, apostrophes and ampersands. Place backslash before the characters to make it display.
Example:
document.write "I m a "good" boy"
document.write "I m a \"good\" boy"
What are JavaScript Cookies?
Cookies are the small test files stored in a computer and it gets created when the user visits the websites to store information that they need. Example could be User Name details and shopping cart information from the previous visits.
Explain what is pop()method in JavaScript?
The pop() method is similar as the shift() method but the difference is that the Shift method works at the start of the array. Also the pop() method take the last element off of the given array and returns it. The array on which is called is then altered.
Example:
var cloths = [“Shirt”, “Pant”, “TShirt”];
cloths.pop();
//Now cloth becomes Shirt,Pant
Whether JavaScript has concept level scope?
No. JavaScript does not have concept level scope. The variable declared inside the function has scope inside the function.
Mention what is the disadvantage of using innerHTML in JavaScript?
If you use innerHTML in JavaScript the disadvantage is
Content is replaced everywhere
We cannot use like “appending to innerHTML”
Even if you use +=like “innerHTML = innerHTML + ‘html’” still the old content is replaced by html
The entire innerHTML content is re-parsed and build into elements, therefore its much slower
The innerHTML does not provide validation and therefore we can potentially insert valid and broken HTML in the document and break it
What is break and continue statements?
Break statement exits from the current loop.
Continue statement continues with next statement of the loop.
What are the two basic groups of dataypes in JavaScript?
They are as –
Primitive
Reference types.
Primitive types are number and Boolean data types. Reference types are more complex types like strings and dates.
Write a simple function (less than 160 characters) that returns a boolean indicating whether or not a string is a palindrome.
The following one line function will return true if str is a palindrome; otherwise, it returns false.
function isPalindrome(str) {
str = str.replace(/\W/g, '').toLowerCase();
return (str == str.split('').reverse().join(''));
}
For example:
console.log(isPalindrome("level")); // logs 'true'
console.log(isPalindrome("levels")); // logs 'false'
console.log(isPalindrome("A car, a man, a maraca")); // logs 'true'
Write a sum method which will work properly when invoked using either syntax below.
console.log(sum(2,3)); // Outputs 5
console.log(sum(2)(3)); // Outputs 5
There are (at least) two ways to do this:
METHOD 1
function sum(x) {
if (arguments.length == 2) {
return arguments[0] + arguments[1];
} else {
return function(y) { return x + y; };
}
}
In JavaScript, functions provide access to an arguments object which provides access to the actual arguments passed to a function. This enables us to use the length property to determine at runtime the number of arguments passed to the function.
If two arguments are passed, we simply add them together and return.
Otherwise, we assume it was called in the form sum(2)(3), so we return an anonymous function that adds together the argument passed to sum() (in this case 2) and the argument passed to the anonymous function (in this case 3).
METHOD 2
function sum(x, y) {
if (y !== undefined) {
return x + y;
} else {
return function(y) { return x + y; };
}
}
When a function is invoked, JavaScript does not require the number of arguments to match the number of arguments in the function definition. If the number of arguments passed exceeds the number of arguments in the function definition, the excess arguments will simply be ignored. On the other hand, if the number of arguments passed is less than the number of arguments in the function definition, the missing arguments will have a value of undefined when referenced within the function. So, in the above example, by simply checking if the 2nd argument is undefined, we can determine which way the function was invoked and proceed accordingly.
Consider the following code snippet:
for (var i = 0; i < 5; i++) {
var btn = document.createElement('button');
btn.appendChild(document.createTextNode('Button ' + i));
btn.addEventListener('click', function(){ console.log(i); });
document.body.appendChild(btn);
}
(a) What gets logged to the console when the user clicks on “Button 4” and why?
(b) Provide one or more alternate implementations that will work as expected.
(a) No matter what button the user clicks the number 5 will always be logged to the console. This is because, at the point that the onclick method is invoked (for any of the buttons), the for loop has already completed and the variable i already has a value of 5. (Bonus points for the interviewee if they know enough to talk about how execution contexts, variable objects, activation objects, and the internal “scope” property contribute to the closure behavior.)
(b) The key to making this work is to capture the value of i at each pass through the for loop by passing it into a newly created function object. Here are four possible ways to accomplish this:
for (var i = 0; i < 5; i++) {
var btn = document.createElement('button');
btn.appendChild(document.createTextNode('Button ' + i));
btn.addEventListener('click', (function(i) {
return function() { console.log(i); };
})(i));
document.body.appendChild(btn);
}
Alternatively, you could wrap the entire call to btn.addEventListener in the new anonymous function:
for (var i = 0; i < 5; i++) {
var btn = document.createElement('button');
btn.appendChild(document.createTextNode('Button ' + i));
(function (i) {
btn.addEventListener('click', function() { console.log(i); });
})(i);
document.body.appendChild(btn);
}
Or, we could replace the for loop with a call to the array object’s native forEach method:
['a', 'b', 'c', 'd', 'e'].forEach(function (value, i) {
var btn = document.createElement('button');
btn.appendChild(document.createTextNode('Button ' + i));
btn.addEventListener('click', function() { console.log(i); });
document.body.appendChild(btn);
});
Lastly, the simplest solution, if you’re in an ES6/ES2015 context, is to use let i instead of var i:
for (let i = 0; i < 5; i++) {
var btn = document.createElement('button');
btn.appendChild(document.createTextNode('Button ' + i));
btn.addEventListener('click', function(){ console.log(i); });
document.body.appendChild(btn);
}
Assuming d is an “empty” object in scope, say:
var d = {};
…what is accomplished using the following code?
[ 'zebra', 'horse' ].forEach(function(k) {
d[k] = undefined;
});
The snippet of code shown above sets two properties on the object d. Ideally, any lookup performed on a JavaScript object with an unset key evaluates to undefined. But running this code marks those properties as “own properties” of the object.
This is a useful strategy for ensuring that an object has a given set of properties. Passing this object to Object.keys will return an array with those set keys as well (even if their values are undefined).
All variables in the JavaScript are object data types.
What is the difference between an alert box and a confirmation box?
An alert box displays only one button which is the OK button.
But a Confirmation box displays two buttons namely OK and cancel.
What are escape characters?
Escape characters (Backslash) is used when working with special characters like single quotes, double quotes, apostrophes and ampersands. Place backslash before the characters to make it display.
Example:
document.write "I m a "good" boy"
document.write "I m a \"good\" boy"
What are JavaScript Cookies?
Cookies are the small test files stored in a computer and it gets created when the user visits the websites to store information that they need. Example could be User Name details and shopping cart information from the previous visits.
Explain what is pop()method in JavaScript?
The pop() method is similar as the shift() method but the difference is that the Shift method works at the start of the array. Also the pop() method take the last element off of the given array and returns it. The array on which is called is then altered.
Example:
var cloths = [“Shirt”, “Pant”, “TShirt”];
cloths.pop();
//Now cloth becomes Shirt,Pant
Whether JavaScript has concept level scope?
No. JavaScript does not have concept level scope. The variable declared inside the function has scope inside the function.
Mention what is the disadvantage of using innerHTML in JavaScript?
If you use innerHTML in JavaScript the disadvantage is
Content is replaced everywhere
We cannot use like “appending to innerHTML”
Even if you use +=like “innerHTML = innerHTML + ‘html’” still the old content is replaced by html
The entire innerHTML content is re-parsed and build into elements, therefore its much slower
The innerHTML does not provide validation and therefore we can potentially insert valid and broken HTML in the document and break it
What is break and continue statements?
Break statement exits from the current loop.
Continue statement continues with next statement of the loop.
What are the two basic groups of dataypes in JavaScript?
They are as –
Primitive
Reference types.
Primitive types are number and Boolean data types. Reference types are more complex types like strings and dates.
Write a simple function (less than 160 characters) that returns a boolean indicating whether or not a string is a palindrome.
The following one line function will return true if str is a palindrome; otherwise, it returns false.
function isPalindrome(str) {
str = str.replace(/\W/g, '').toLowerCase();
return (str == str.split('').reverse().join(''));
}
For example:
console.log(isPalindrome("level")); // logs 'true'
console.log(isPalindrome("levels")); // logs 'false'
console.log(isPalindrome("A car, a man, a maraca")); // logs 'true'
Write a sum method which will work properly when invoked using either syntax below.
console.log(sum(2,3)); // Outputs 5
console.log(sum(2)(3)); // Outputs 5
There are (at least) two ways to do this:
METHOD 1
function sum(x) {
if (arguments.length == 2) {
return arguments[0] + arguments[1];
} else {
return function(y) { return x + y; };
}
}
In JavaScript, functions provide access to an arguments object which provides access to the actual arguments passed to a function. This enables us to use the length property to determine at runtime the number of arguments passed to the function.
If two arguments are passed, we simply add them together and return.
Otherwise, we assume it was called in the form sum(2)(3), so we return an anonymous function that adds together the argument passed to sum() (in this case 2) and the argument passed to the anonymous function (in this case 3).
METHOD 2
function sum(x, y) {
if (y !== undefined) {
return x + y;
} else {
return function(y) { return x + y; };
}
}
When a function is invoked, JavaScript does not require the number of arguments to match the number of arguments in the function definition. If the number of arguments passed exceeds the number of arguments in the function definition, the excess arguments will simply be ignored. On the other hand, if the number of arguments passed is less than the number of arguments in the function definition, the missing arguments will have a value of undefined when referenced within the function. So, in the above example, by simply checking if the 2nd argument is undefined, we can determine which way the function was invoked and proceed accordingly.
Consider the following code snippet:
for (var i = 0; i < 5; i++) {
var btn = document.createElement('button');
btn.appendChild(document.createTextNode('Button ' + i));
btn.addEventListener('click', function(){ console.log(i); });
document.body.appendChild(btn);
}
(a) What gets logged to the console when the user clicks on “Button 4” and why?
(b) Provide one or more alternate implementations that will work as expected.
(a) No matter what button the user clicks the number 5 will always be logged to the console. This is because, at the point that the onclick method is invoked (for any of the buttons), the for loop has already completed and the variable i already has a value of 5. (Bonus points for the interviewee if they know enough to talk about how execution contexts, variable objects, activation objects, and the internal “scope” property contribute to the closure behavior.)
(b) The key to making this work is to capture the value of i at each pass through the for loop by passing it into a newly created function object. Here are four possible ways to accomplish this:
for (var i = 0; i < 5; i++) {
var btn = document.createElement('button');
btn.appendChild(document.createTextNode('Button ' + i));
btn.addEventListener('click', (function(i) {
return function() { console.log(i); };
})(i));
document.body.appendChild(btn);
}
Alternatively, you could wrap the entire call to btn.addEventListener in the new anonymous function:
for (var i = 0; i < 5; i++) {
var btn = document.createElement('button');
btn.appendChild(document.createTextNode('Button ' + i));
(function (i) {
btn.addEventListener('click', function() { console.log(i); });
})(i);
document.body.appendChild(btn);
}
Or, we could replace the for loop with a call to the array object’s native forEach method:
['a', 'b', 'c', 'd', 'e'].forEach(function (value, i) {
var btn = document.createElement('button');
btn.appendChild(document.createTextNode('Button ' + i));
btn.addEventListener('click', function() { console.log(i); });
document.body.appendChild(btn);
});
Lastly, the simplest solution, if you’re in an ES6/ES2015 context, is to use let i instead of var i:
for (let i = 0; i < 5; i++) {
var btn = document.createElement('button');
btn.appendChild(document.createTextNode('Button ' + i));
btn.addEventListener('click', function(){ console.log(i); });
document.body.appendChild(btn);
}
Assuming d is an “empty” object in scope, say:
var d = {};
…what is accomplished using the following code?
[ 'zebra', 'horse' ].forEach(function(k) {
d[k] = undefined;
});
The snippet of code shown above sets two properties on the object d. Ideally, any lookup performed on a JavaScript object with an unset key evaluates to undefined. But running this code marks those properties as “own properties” of the object.
This is a useful strategy for ensuring that an object has a given set of properties. Passing this object to Object.keys will return an array with those set keys as well (even if their values are undefined).
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