JavaScript Interview Questions & Answers for Intermediate
What are all the looping structures in JavaScript ?
- while loop: A while loop is a control flow statement that allows code to be executed repeatedly based on a given Boolean condition. The while loop can be thought of as a repeating if statement.
- for loop: A for loop provides a concise way of writing the loop structure. Unlike a while loop, for statement consumes the initialization, condition and increment/decrement in one line thereby providing a shorter, easy to debug structure of looping.
- do while: A do-while loop is similar to while loop with the only difference that it checks the condition after executing the statements, and therefore is an example of Exit Control Loop.
How can the style/class of an element be changed?
To change the style/class of an element there are two possible ways. We use document.getElementByID method
document.getElementById("myText").style.fontSize = "16px;
document.getElementById("myText").className = "class";
Explain how to read and write a file using JavaScript?
The readFile() functions is used for reading operation.
readFile( Path, Options, Callback)
The writeFile() functions is used for writing operation.
writeFile( Path, Data, Callback)
What is called Variable typing in JavaScript?
The variable typing is the type of variable used to store a number and using that same variable to assign a “string”.
Geeks = 42;
Geeks = "GeeksforGeeks";
How to convert the string of any base to integer in JavaScript?
In JavaScript, parseInt() function is used to convert the string to an integer. This function returns an integer of base which is specified in second argument of parseInt() function. The parseInt() function returns Nan (not a number) when the string doesn’t contain number.
Explain how to detect the operating system on the client machine?
To detect the operating system on the client machine, one can simply use navigator.appVersion or navigator.userAgent property. The Navigator appVersion property is a read-only property and it returns the string that represents the version information of the browser.
What are the types of Pop up boxes available in JavaScript?
There are three types of pop boxes available in JavaScript.
What is the difference between an alert box and a confirmation box?
An alert box will display only one button which is the OK button. It is used to inform the user about the agreement has to agree. But a Confirmation box displays two buttons OK and cancel, where the user can decide to agree or not.
What is the disadvantage of using innerHTML in JavaScript?
There are lots of disadvantages of using the innerHTML in JavaScript as the content will replace everywhere. If you use += like “innerHTML = innerHTML + ‘html’” still the old content is replaced by HTML. It preserves event handlers attached to any DOM elements.
What is the use of void(0)?
The void(0) is used to call another method without refreshing the page during the calling time parameter “zero” will be passed.
JavaScript Interview Questions for Experienced
What is the ‘Strict’ mode in JavaScript and how can it be enabled?
Strict Mode is a new feature in ECMAScript 5 that allows you to place a program or a function in a “strict” operating context. This strict context prevents certain actions from being taken and throws more exceptions. The statement “use strict” instructs the browser to use the Strict mode, which is a reduced and safer feature set of JavaScript.
How to get the status of a CheckBox?
The DOM Input Checkbox Property is used to set or return the checked status of a checkbox field. This property is used to reflect the HTML Checked attribute.
document.getElementById("GFG").checked;
If the CheckBox is checked then it returns True.
How to explain closures in JavaScript and when to use it?
The closure is created when a child functions to keep the environment of the parent’s scope even after the parent’s function has already executed. The Closure is a locally declared variable related to a function. The closure will provide better control over the code when using them.
What is the difference between call() and apply() methods ?
Both methods are used in a different situation
- call() Method: It calls the method, taking the owner object as argument. The keyword this refers to the ‘owner’ of the function or the object it belongs to. We can call a method that can be used on different objects.
- apply() Method: The apply() method is used to write methods, which can be used on different objects. It is different from the function call() because it takes arguments as an array.
How to target a particular frame from a hyperlink in JavaScript?
This can be done by using the target attribute in the hyperlink. Like
New Page
Write the errors shown in JavaScript?
There are three different types of errors in JavaScript.
- Syntax error: A syntax error is an error in the syntax of a sequence of characters or tokens that are intended to be written in a particular programming language.
- Logical error: It is the most difficult error to be traced as it is the error on the logical part of the coding or logical error is a bug in a program that causes to operate incorrectly and terminate abnormally.
- Runtime Error: A runtime error is an error that occurs during the running of the program, also known as an exception.
What is the difference between JavaScript and Jscript?
JavaScript
- It is a scripting language developed by Netscape.
- It is used to design client and server-side applications.
- It is completely independent of Java language.
Jscript
- It is a scripting language developed by Microsoft.
- It is used to design active online content for the word wide Web.
What does var myArray = [[]]; statement declares?
In JavaScript, this statement is used to declare a two-dimensional array.
How many ways an HTML element can be accessed in JavaScript code?
There are four possible ways to access HTML elements in JavaScript which are:
- getElementById() Method: It is used to get the element by its id name.
- getElementsByClass() Method: It is used to get all the elements that have the given classname.
- getElementsByTagName() Method: It is used to get all the elements that have the given tag name.
- querySelector() Method: This function takes CSS style selector and returns the first selected element.
What is the difference between innerHTML & innerText?
The innerText property sets or returns the text content as plain text of the specified node, and all its descendants whereas the innerHTML property sets or returns the plain text or HTML contents in the elements. Unlike innerText, inner HTML lets you work with HTML rich text and doesn’t automatically encode and decode text.
What is an event bubbling in JavaScript?
Consider a situation an element is present inside another element and both of them handle an event. When an event occurs in bubbling, the innermost element handles the event first, then the outer, and so on.