Pegasystems Most Frequently Asked Latest JavaScript Interview Questions Answers
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.
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.
How are object properties assigned?
Assigning properties to objects is done in the same way as a value is assigned to a variable. For example, a form object’s action value is assigned as ‘submit’ in the following manner – Document.form.action=”submit”
What is the method for reading and writing a file in JavaScript?
This can be done by Using JavaScript extensions (runs from JavaScript Editor), example for opening of a file –
fh = fopen(getScriptPath(), 0);
How are DOM utilized in JavaScript?
DOM stands for Document Object Model and is responsible for how various objects in a document interact with each other. DOM is required for developing web pages, which includes objects like paragraph, links, etc. These objects can be operated to include actions like add or delete. DOM is also required to add extra capabilities to a web page. On top of that, the use of API gives an advantage over other existing models.
How are event handlers utilized in JavaScript?
Events are the actions that result from activities, such as clicking a link or filling a form, by the user. An event handler is required to manage proper execution of all these events. Event handlers are an extra attribute of the object. This attribute includes event’s name and the action taken if the event takes place.
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();
 |
| Pegasystems Most Frequently Asked Latest JavaScript Interview Questions Answers |
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.
How are object properties assigned?
Assigning properties to objects is done in the same way as a value is assigned to a variable. For example, a form object’s action value is assigned as ‘submit’ in the following manner – Document.form.action=”submit”
What is the method for reading and writing a file in JavaScript?
This can be done by Using JavaScript extensions (runs from JavaScript Editor), example for opening of a file –
fh = fopen(getScriptPath(), 0);
How are DOM utilized in JavaScript?
DOM stands for Document Object Model and is responsible for how various objects in a document interact with each other. DOM is required for developing web pages, which includes objects like paragraph, links, etc. These objects can be operated to include actions like add or delete. DOM is also required to add extra capabilities to a web page. On top of that, the use of API gives an advantage over other existing models.
How are event handlers utilized in JavaScript?
Events are the actions that result from activities, such as clicking a link or filling a form, by the user. An event handler is required to manage proper execution of all these events. Event handlers are an extra attribute of the object. This attribute includes event’s name and the action taken if the event takes place.
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