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.
How can a particular frame be targeted, from a hyperlink, in JavaScript?
This can be done by including the name of the required frame in the hyperlink using the ‘target’ attribute.
<a href=”newpage.htm” target=”newframe”>>New Page</a>
What is the role of break and continue statements?
Break statement is used to come out of the current loop while the continue statement continues the current loop with a new recurrence.
Write the point of difference between web-garden and a web-farm?
Both web-garden and web-farm are web hosting systems. The only difference is that web-garden is a setup that includes many processors in a single server while web-farm is a larger setup that uses more than one server.
What would be the result of 3+2+”7″?
Since 3 and 2 are integers, they will be added numerically. And since 7 is a string, its concatenation will be done. So the result would be 57.
Explain how to detect the operating system on the client machine?
In order to detect the operating system on the client machine, the navigator.appVersion string (property) should be used.
What do mean by NULL in Javascript?
The NULL value is used to represent no value or no object. It implies no object or null string, no valid boolean value, no number and no array object.
What is the function of delete operator?
The functionality of delete operator is used to delete all variables and objects in a program but it cannot delete variables declared with VAR keyword.
What is an undefined value in JavaScript?
Undefined value means the
Variable used in the code doesn’t exist
Variable is not assigned to any value
Property doesn’t exist
What are all the types of Pop up boxes available in JavaScript?
Alert
Confirm and
Prompt
What is the use of Void(0)?
Void(0) is used to prevent the page from refreshing and parameter “zero” is passed while calling.
Void(0) is used to call another method without refreshing the page.
How can a page be forced to load another page in JavaScript?
The following code has to be inserted to achieve the desired effect:
<script language="JavaScript" type="text/javascript" >
<!-- location.href="http://newhost/newpath/newfile.html"; //--></script>
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.
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.
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| CGI Group JavaScript Most Frequently Asked Latest Interview Questions Answers |
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.
How can a particular frame be targeted, from a hyperlink, in JavaScript?
This can be done by including the name of the required frame in the hyperlink using the ‘target’ attribute.
<a href=”newpage.htm” target=”newframe”>>New Page</a>
What is the role of break and continue statements?
Break statement is used to come out of the current loop while the continue statement continues the current loop with a new recurrence.
Write the point of difference between web-garden and a web-farm?
Both web-garden and web-farm are web hosting systems. The only difference is that web-garden is a setup that includes many processors in a single server while web-farm is a larger setup that uses more than one server.
What would be the result of 3+2+”7″?
Since 3 and 2 are integers, they will be added numerically. And since 7 is a string, its concatenation will be done. So the result would be 57.
Explain how to detect the operating system on the client machine?
In order to detect the operating system on the client machine, the navigator.appVersion string (property) should be used.
What do mean by NULL in Javascript?
The NULL value is used to represent no value or no object. It implies no object or null string, no valid boolean value, no number and no array object.
What is the function of delete operator?
The functionality of delete operator is used to delete all variables and objects in a program but it cannot delete variables declared with VAR keyword.
What is an undefined value in JavaScript?
Undefined value means the
Variable used in the code doesn’t exist
Variable is not assigned to any value
Property doesn’t exist
What are all the types of Pop up boxes available in JavaScript?
Alert
Confirm and
Prompt
What is the use of Void(0)?
Void(0) is used to prevent the page from refreshing and parameter “zero” is passed while calling.
Void(0) is used to call another method without refreshing the page.
How can a page be forced to load another page in JavaScript?
The following code has to be inserted to achieve the desired effect:
<script language="JavaScript" type="text/javascript" >
<!-- location.href="http://newhost/newpath/newfile.html"; //--></script>
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.