CISCO Systems JavaScript Most Frequently Asked Latest Interview Questions Answers
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.
What is the ‘Strict’ mode in JavaScript and how can it be enabled?
Strict Mode adds certain compulsions to JavaScript. Under the strict mode, JavaScript shows errors for a piece of codes, which did not show an error before, but might be problematic and potentially unsafe. Strict mode also solves some mistakes that hamper the JavaScript engines to work efficiently.
Strict mode can be enabled by adding the string literal “use strict” above the file. This can be illustrated by the given example:
function myfunction()
{
“use strict";
var v = “This is a strict mode function";
}
What is the way to get the status of a CheckBox?
The status can be acquired as follows –
alert(document.getElementById(‘checkbox1′).checked);
If the CheckBox will be checked, this alert will return TRUE.
How can the OS of the client machine be detected?
The navigator.appVersion string can be used to detect the operating system on the client machine.
Explain window.onload and onDocumentReady?
The onload function is not run until all the information on the page is loaded. This leads to a substantial delay before any code is executed.
onDocumentReady loads the code just after the DOM is loaded. This allows early manipulation of the code.
How will you explain closures in JavaScript? When are they used?
Closure is a locally declared variable related to a function which stays in memory when the function has returned.
For example:
function greet(message) {
console.log(message);
}
function greeter(name, age) {
return name + " says howdy!! He is " + age + " years old";
}
// Generate the message
var message = greeter("James", 23);
// Pass it explicitly to greet
greet(message);
This function can be better represented by using closures
function greeter(name, age) {
var message = name + " says howdy!! He is " + age + " years old";
return function greet() {
console.log(message);
};
}
// Generate the closure
var JamesGreeter = greeter("James", 23);
// Use the closure
JamesGreeter();
How can a value be appended to an array?
A value can be appended to an array in the given manner –
arr[arr.length] = value;
Explain the for-in loop?
The for-in loop is used to loop through the properties of an object.
The syntax for the for-in loop is –
for (variable name in object){
statement or block to execute
}
In each repetition, one property from the object is associated to the variable name, and the loop is continued till all the properties of the object are depleted.
Describe the properties of an anonymous function in JavaScript?
A function that is declared without any named identifier is known as an anonymous function. In general, an anonymous function is inaccessible after its declaration.
Anonymous function declaration –
var anon = function() {
alert('I am anonymous');
};
anon();
What is the difference between .call() and .apply()?
The function .call() and .apply() are very similar in their usage except a little difference. .call() is used when the number of the function’s arguments are known to the programmer, as they have to be mentioned as arguments in the call statement. On the other hand, .apply() is used when the number is not known. The function .apply() expects the argument to be an array.
The basic difference between .call() and .apply() is in the way arguments are passed to the function. Their usage can be illustrated by the given example.
var someObject = {
myProperty : 'Foo',
myMethod : function(prefix, postfix) {
alert(prefix + this.myProperty + postfix);
}
};
someObject.myMethod('<', '>'); // alerts '<Foo>'
var someOtherObject = {
myProperty : 'Bar'
};
someObject.myMethod.call(someOtherObject, '<', '>'); // alerts '<Bar>'
someObject.myMethod.apply(someOtherObject, ['<', '>']); // alerts '<Bar>'
Define event bubbling?
JavaScript allows DOM elements to be nested inside each other. In such a case, if the handler of the child is clicked, the handler of parent will also work as if it were clicked too.
Is JavaScript case sensitive? Give an example?
Yes, JavaScript is case sensitive. For example, a function parseInt is not same as the function Parseint.
What boolean operators can be used in JavaScript?
The ‘And’ Operator (&&), ‘Or’ Operator (||) and the ‘Not’ Operator (!) can be used in JavaScript.
*Operators are without the parenthesis.
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.
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| CISCO Systems JavaScript Most Frequently Asked Latest Interview Questions Answers |
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.
What is the ‘Strict’ mode in JavaScript and how can it be enabled?
Strict Mode adds certain compulsions to JavaScript. Under the strict mode, JavaScript shows errors for a piece of codes, which did not show an error before, but might be problematic and potentially unsafe. Strict mode also solves some mistakes that hamper the JavaScript engines to work efficiently.
Strict mode can be enabled by adding the string literal “use strict” above the file. This can be illustrated by the given example:
function myfunction()
{
“use strict";
var v = “This is a strict mode function";
}
What is the way to get the status of a CheckBox?
The status can be acquired as follows –
alert(document.getElementById(‘checkbox1′).checked);
If the CheckBox will be checked, this alert will return TRUE.
How can the OS of the client machine be detected?
The navigator.appVersion string can be used to detect the operating system on the client machine.
Explain window.onload and onDocumentReady?
The onload function is not run until all the information on the page is loaded. This leads to a substantial delay before any code is executed.
onDocumentReady loads the code just after the DOM is loaded. This allows early manipulation of the code.
How will you explain closures in JavaScript? When are they used?
Closure is a locally declared variable related to a function which stays in memory when the function has returned.
For example:
function greet(message) {
console.log(message);
}
function greeter(name, age) {
return name + " says howdy!! He is " + age + " years old";
}
// Generate the message
var message = greeter("James", 23);
// Pass it explicitly to greet
greet(message);
This function can be better represented by using closures
function greeter(name, age) {
var message = name + " says howdy!! He is " + age + " years old";
return function greet() {
console.log(message);
};
}
// Generate the closure
var JamesGreeter = greeter("James", 23);
// Use the closure
JamesGreeter();
How can a value be appended to an array?
A value can be appended to an array in the given manner –
arr[arr.length] = value;
Explain the for-in loop?
The for-in loop is used to loop through the properties of an object.
The syntax for the for-in loop is –
for (variable name in object){
statement or block to execute
}
In each repetition, one property from the object is associated to the variable name, and the loop is continued till all the properties of the object are depleted.
Describe the properties of an anonymous function in JavaScript?
A function that is declared without any named identifier is known as an anonymous function. In general, an anonymous function is inaccessible after its declaration.
Anonymous function declaration –
var anon = function() {
alert('I am anonymous');
};
anon();
What is the difference between .call() and .apply()?
The function .call() and .apply() are very similar in their usage except a little difference. .call() is used when the number of the function’s arguments are known to the programmer, as they have to be mentioned as arguments in the call statement. On the other hand, .apply() is used when the number is not known. The function .apply() expects the argument to be an array.
The basic difference between .call() and .apply() is in the way arguments are passed to the function. Their usage can be illustrated by the given example.
var someObject = {
myProperty : 'Foo',
myMethod : function(prefix, postfix) {
alert(prefix + this.myProperty + postfix);
}
};
someObject.myMethod('<', '>'); // alerts '<Foo>'
var someOtherObject = {
myProperty : 'Bar'
};
someObject.myMethod.call(someOtherObject, '<', '>'); // alerts '<Bar>'
someObject.myMethod.apply(someOtherObject, ['<', '>']); // alerts '<Bar>'
Define event bubbling?
JavaScript allows DOM elements to be nested inside each other. In such a case, if the handler of the child is clicked, the handler of parent will also work as if it were clicked too.
Is JavaScript case sensitive? Give an example?
Yes, JavaScript is case sensitive. For example, a function parseInt is not same as the function Parseint.
What boolean operators can be used in JavaScript?
The ‘And’ Operator (&&), ‘Or’ Operator (||) and the ‘Not’ Operator (!) can be used in JavaScript.
*Operators are without the parenthesis.
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