What are the pre-requisites to execute AJAX applications on a server?
AJAX is a built-in functionality of .NET Framework 4.0 and AJAX application can be executed by just installing Microsoft Visual Studio 2010. To use extenders in your applications, you are required to install AJAX Control Toolkit and copy the AjaxControlToolkit.dll file to the Bin directory of your application.
Which request is better, Get or Post?
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.
How many update panel can be used per page?
There are no restrictions on the number of update panels per page.
How can you find out that an AJAX request has been completed?
ReadyState property is used to check whether AJAX request has been completed. If the property is equal to four, then the request has been completed and data is available.
Is javascript knowledge is required to do Ajax?
Yes, if you plan to develop new AJAX functionality for your web application.
What are all the browsers support AJAX?
Following browsers support AJAX:
Internet Explorer 5.0 and above
Opera 7.6 and above
Netscape 7.1 and above
Safari 1.2 and above
How can you test the Ajax code?
JSUnit is the client side javascript code used as part of JUnit. JSUnit has been used for Ajax code.
Is Ajax said to be a technology platform or is it an architectural style?
Ajax supports both technology and as architectural style.
How can AJAX applications be debugged?
Two tools are used for debugging:
Fiddler for IE
Firebug for Mozilla.
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.
AJAX is a built-in functionality of .NET Framework 4.0 and AJAX application can be executed by just installing Microsoft Visual Studio 2010. To use extenders in your applications, you are required to install AJAX Control Toolkit and copy the AjaxControlToolkit.dll file to the Bin directory of your application.
Which request is better, Get or Post?
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.
 |
| CDW Most Frequently Asked Latest JavaScript Interview Questions Answers |
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.
How many update panel can be used per page?
There are no restrictions on the number of update panels per page.
How can you find out that an AJAX request has been completed?
ReadyState property is used to check whether AJAX request has been completed. If the property is equal to four, then the request has been completed and data is available.
Is javascript knowledge is required to do Ajax?
Yes, if you plan to develop new AJAX functionality for your web application.
What are all the browsers support AJAX?
Following browsers support AJAX:
Internet Explorer 5.0 and above
Opera 7.6 and above
Netscape 7.1 and above
Safari 1.2 and above
How can you test the Ajax code?
JSUnit is the client side javascript code used as part of JUnit. JSUnit has been used for Ajax code.
Is Ajax said to be a technology platform or is it an architectural style?
Ajax supports both technology and as architectural style.
How can AJAX applications be debugged?
Two tools are used for debugging:
Fiddler for IE
Firebug for Mozilla.
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).