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JavaScript Interview Questions and Answers- Part 5
LISTEN TO THE JAVASCRIPT FAQs LIKE AN AUDIOBOOK
If you’ve already passed the initial technical screen, the final interview rounds usually focus on more complex coding problems and deeper JavaScript questions. That’s where this second part of our JavaScript interview Q&A guide comes in. It’s tailored for developers preparing for onsite or advanced interviews where understanding code behavior, performance implications, and debugging skills becomes essential.
Topics covered include memory management, scope chain, closures, and how JavaScript handles asynchronous operations—questions that not only test your theoretical knowledge but also your ability to think like a developer. If you’re preparing for roles such as React developer, Node.js engineer, or full stack developer, mastering these questions can give you the edge you need. Use this blog as your revision checklist before your next interview. Understanding these questions and practicing your explanations will help you communicate clearly and solve problems under pressure.
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exec () is used to find and extract matches from a string using regular expressions and provides more detailed information about the match, while test () is used to simply check if a pattern exists in a string and returns a boolean value.
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Following loops are available in JavaScript:
- While loop
- Do-while loops
- For loop statement
- for..in loop
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The unshift() method is a JavaScript array method is used to add one or more elements to the beginning (start) of an array. It modifies the original array and returns the new length of the array.
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In JavaScript, the unescape() and escape() functions are used for encoding and decoding special characters in strings. However, it’s important to note that these functions are considered deprecated and should not be used in modern JavaScript code. Instead, you should use decodeURI(), encodeURI(), decodeURIComponent(), and encodeURIComponent() for similar purposes.
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In JavaScript, decodeURI() and encodeURI() are two functions used to manipulate Uniform Resource Identifiers (URIs) or URLs. They are primarily used for handling special characters and encoding/decoding them to ensure the integrity of the URI.
- encodeURI(): This function is used to encode a complete URI or URL, making sure that any reserved or special characters within the URI are converted into a format that is safe for inclusion in a URL. It does not encode characters that have a specific meaning in a URL, such as colons (for specifying a port) or forward slashes (for path separators).
- decodeURI(): This function is used to decode a URI or URL that has been previously encoded using encodeURI(). It reverses the encoding process, converting the encoded characters back to their original form.
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QuickSort is a popular sorting algorithm that can be implemented in JavaScript and many other programming languages. It’s known for its efficiency and is often used in practice. QuickSort works by selecting a “pivot” element from the array and partitioning the other elements into two sub-arrays, according to whether they are less than or greater than the pivot. The sub-arrays are then sorted recursively. This process continues until the entire array is sorted.
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In JavaScript, the pop() method is used to remove and return the last element from an array. It modifies the original array by removing the last element and then returns the removed element.
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Following are the two primary groups of data types in JavaScript:
- Primitive Types
- Reference Types
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In JavaScript, you can create generic objects in several ways. Here are two common approaches:
- Using Object Literals: The simplest way to create a generic object in JavaScript is by using object literals. Object literals are key-value pairs enclosed in curly braces {}.
- Using the Object Constructor: Another way to create generic objects is by using the Object constructor function. You can use the new keyword with Object to create an empty object and then add properties and values to it.
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In JavaScript, variable typing, also known as dynamic typing or weak typing, refers to how data types are determined and handled for variables. Unlike some other programming languages that have static typing, where you declare the data type of a variable explicitly, JavaScript determines the data type of a variable dynamically based on the value assigned to it.
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The unshift() method in JavaScript is used to add one or more elements to the beginning of an array. It modifies the original array and returns the new length of the array.
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JavaScript and JScript are both scripting languages used for web development, but they have some differences:
- Origin:
- JavaScript: JavaScript was developed by Netscape Communications Corporation and was initially released in 1995. It has since become a widely used scripting language for web development.
- JScript: JScript is Microsoft’s implementation of ECMAScript, the scripting language specification that JavaScript also adheres to. It was primarily used in Microsoft’s Internet Explorer browser.
- Compatibility:
- JavaScript: JavaScript is a widely supported scripting language that can run in almost all web browsers, including Chrome, Firefox, Safari, and Edge.
- JScript: JScript was primarily designed for Internet Explorer and may not work as expected in other browsers. With the decline of Internet Explorer and the adoption of modern web standards, JScript has become less relevant.
- Features:
- JavaScript: JavaScript adheres closely to the ECMAScript standard, which defines the core features and functionality of the language. It has a large and active developer community, leading to continuous updates and improvements.
- JScript: JScript is based on an earlier version of ECMAScript and lacks some of the features and improvements found in modern JavaScript. It may not support the latest web development standards and practices.
- Usage:
- JavaScript: JavaScript is used extensively in web development for creating interactive and dynamic web applications. It can be used for both client-side scripting (in web browsers) and server-side scripting (with technologies like Node.js).
- JScript: JScript was primarily used for client-side scripting in Internet Explorer for older web applications. As Internet Explorer usage has declined, the usage of JScript has also decreased.
- Popularity:
- JavaScript: JavaScript is one of the most popular and widely used programming languages in the world. It has a large community of developers, extensive libraries and frameworks, and is a fundamental language for web development.
- JScript: JScript is not as popular or widely used as JavaScript, mainly due to its ties to Internet Explorer and the decline of that browser.
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An anonymous function is a function that does not have a specified name. Instead of being declared with a name like traditional functions, anonymous functions are defined inline as expressions. They are often used when you need a small, short-lived function for a specific task and don’t want to clutter your code with unnecessary function names.
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JavaScript is a dynamically typed language. This means that variable types are determined at runtime rather than at compile time. In JavaScript, you can assign different types of values to a variable without specifying its type explicitly. The type of a variable can change during the execution of a program. This dynamic typing flexibility can be both a strength and a potential source of errors in JavaScript programming.
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Optimizing JavaScript performance is crucial for creating fast and efficient web applications. Here are some best practices to help you achieve better JavaScript performance:
- Minimize HTTP Requests
- Use Async and Defer Attributes
- Reduce DOM Manipulation
- Optimize Loops and Iterations
- Use Efficient Libraries
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Using innerHTML in JavaScript can be convenient for manipulating the content of HTML elements, but it also has several disadvantages, such as:
- Security Risks: One of the most significant drawbacks is the potential for cross-site scripting (XSS) attacks. If you insert user-generated content directly into an element’s innerHTML, malicious code can be injected and executed within your page, compromising security.
- Performance Issues: Manipulating innerHTML can be slower than other DOM manipulation methods like createElement and appendChild. This is because when you set innerHTML, the browser must parse the entire HTML content and rebuild the DOM tree, which can be resource-intensive for complex documents.
- Event Handlers: If you replace the content of an element using innerHTML, any event handlers attached to the previous content may be lost. You’ll need to reattach event listeners to the new elements, which can be cumbersome.
- Script Execution: Scripts within the new HTML content inserted via innerHTML are not re-evaluated. This means that any JavaScript in the inserted content won’t be executed unless you explicitly do so, which can lead to unexpected behavior.
- Limited Control: When you use innerHTML, you’re essentially replacing the entire content of an element. This can make it challenging to make precise changes to the DOM, as you’re working with strings of HTML rather than individual elements.
- Accessibility Issues: Manipulating innerHTML can disrupt the accessibility of a web page. Screen readers may not recognize changes made with innerHTML, making your content less accessible to users with disabilities.
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The “screen objects” typically refer to properties and methods related to the user’s screen or monitor within a web browser. These objects are part of the Window object and provide information about the user’s screen dimensions, pixel density, and more.
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The deferred scripts in JavaScript provide a way to load and execute scripts asynchronously while ensuring they run in a specific order and after the HTML document has been fully parsed. This can lead to better performance and a smoother user experience for web applications.
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In JavaScript, void(0) is often used as a way to create a statement that evaluates to the undefined value. Its primary use is to prevent the browser from navigating to a new page when clicking on a link or button with a href or onclick attribute.