JavaScript Interview Questions and Answers- Part 2

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You can place your JavaScript code inside the DOMContentLoaded event handler to ensure it runs after the HTML content is loaded but before all external resources like images and stylesheets are fully loaded.

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This refers to the current context or object. Its value depends on how and where a function is called. In a global context, it refers to the global object (e.g., window in a browser). In a method, it refers to the object the method was called on.

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== is used for loose equality and performs type coercion, while === is used for strict equality and does not perform type coercion. In most cases, it’s recommended to use === for comparisons.

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async/await is used for asynchronous programming in JavaScript. async defines a function as asynchronous, and await is used inside an async function to pause execution until a promise is resolved.

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Let and const are block-scoped, while var is function-scoped. const is used for constant values that cannot be reassigned, while let allows reassignment.

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A closure is a function that has access to its own scope, the outer function’s scope, and the global scope. It allows for encapsulation and data hiding.

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The Event Loop is a mechanism in JavaScript that handles asynchronous operations. It continuously checks the call stack and the callback queue, ensuring that asynchronous tasks are executed when the call stack is empty.

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To delete a cookie using JavaScript, you can use the document.cookie property to set the cookie’s expiration date to a date in the past. This effectively removes the cookie from the user’s browser.

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A debugger in JavaScript is a crucial tool for developers to identify and fix errors or bugs in their JavaScript code. It allows developers to step through their code, inspect variables, and track the flow of execution to pinpoint and understand issues in their programs.

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Implicit type coercion in JavaScript refers to the automatic conversion of data types during various operations, such as arithmetic, comparisons, and string concatenation, without the need for explicit conversion by the developer. JavaScript is a loosely typed language, which means it allows for this kind of type coercion to make operations more flexible.

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In JavaScript, the terms “attributes” and “properties” are often used interchangeably, but they have distinct meanings depending on the context. Let’s clarify the difference between them:

1. Attributes:
   • Attributes are usually associated with HTML elements in the context of web development.
   • They are defined in the HTML markup as part of an element’s tag.
   • Attributes provide additional information about an element and are typically used for configuring or specifying initial values.
   • Examples of HTML attributes include src, href, class, id, and custom data attributes like data-myattribute.
2. Properties:
   • Properties, on the other hand, are related to JavaScript objects, including HTML DOM objects.
   • They are accessed and manipulated through JavaScript code and represent the current state of an element or object.
   • Properties can change dynamically as a result of user interaction or JavaScript code execution.
   • For HTML DOM elements, properties represent the current state of the element, such as textContent, innerHTML, value, style, etc.

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There are mainly three different ways in which a JavaScript code can be involved in the HTML file, such as:

• Internal
• External
• Inline

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In JavaScript, higher-order functions are functions that can accept other functions as arguments, return functions as values, or both. These functions treat functions as first-class citizens, allowing you to work with them in a flexible and powerful way.

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When we refer to a “typed language,” we are typically talking about the data types or type systems used in the language. JavaScript is often considered a dynamically typed language, which means that variables are not bound to a specific data type when they are declared. Instead, the type of a variable can change at runtime based on the value assigned to it.

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Local storage and session storage are both web storage options available in modern web browsers to store data on the client side for web applications. They share the following differences:

1. Scope of Data:
   • Local Storage: Data stored in local storage persists even after the browser is closed and is not tied to a specific session or tab. It remains available until explicitly removed by the web application or the user.
   • Session Storage: Data stored in session storage is only available for the duration of the page session. It gets cleared when the user closes the browser tab or navigates away from the page.
2. Storage Limit:
   • Local Storage: Typically, local storage provides more storage space compared to session storage. The exact limit varies between browsers but is usually around 5-10 MB per domain.
3. Data Accessibility:
   • Local Storage: Data in local storage is accessible across browser tabs and windows, making it useful for scenarios where you need to persist data between different parts of your web application.
   • Session Storage: Data in session storage is only accessible within the same tab or window where it was stored. It cannot be shared between different tabs or windows.
4. Data Persistence:
   • Local Storage: Data persists even after the user closes the browser and reopens it. It can be used for long-term data storage.
   • Session Storage: Data is only available for the current browsing session. If the user closes the tab or browser, the data is lost.
5. Use Cases:
   • Local Storage: It is commonly used for storing user preferences, settings, or any data that should persist across sessions or tabs.
   • Session Storage: It is useful for temporary data storage, such as keeping track of a user’s progress through a multi-step form or storing temporary authentication tokens.

In summary, the choice between local storage and session storage depends on your specific use case and data persistence requirements. If you need data to persist across sessions and tabs, local storage is more suitable. If you only need data for the current session or page, session storage is a better choice.

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In JavaScript, currying is a functional programming technique that allows you to transform a function that takes multiple arguments into a series of functions that each take a single argument. Currying helps in creating more flexible and reusable functions. Instead of passing all the arguments to a function at once, you can pass them one by one, creating a chain of partially applied functions. Each function in the chain takes one argument and returns a new function that expects the next argument until all the arguments have been provided, and the final result is returned.

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In JavaScript, “undeclared” and “undefined” are two different concepts related to variables and properties:

• Undeclared: An undeclared variable or property is one that has not been declared using a var, let, const, or function When you try to use an undeclared variable or access an undeclared property, JavaScript will throw a ReferenceError. It means the variable or property doesn’t exist in the current scope.
• Undefined: An “undefined” value in JavaScript means that a variable or property has been declared but has not been assigned a value. It is a special value in JavaScript that represents the absence of a value. Variables are initialized with “undefined” by default if you don’t assign them a value.

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The key difference between call and apply is how they accept and pass arguments to the function. call takes arguments individually, while apply takes them as an array. You can choose between them based on your specific use case and how your function expects its arguments to be passed.

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In JavaScript, there are two primary ways to define functions: function declarations and function expressions. Let’s explore the key differences between them:

2. Hoisting:
   • Function Declaration: Function declarations are hoisted to the top of their containing scope. This means you can call a function before it’s declared in your code, and it will still work.
   • Function Expression: Function expressions are not hoisted. You must define the function before calling it; otherwise, you’ll encounter a reference error.
3. Named vs. Anonymous:
4. • Function Declaration: Function declarations have names, making it easy to refer to them within the function itself and throughout your code.
   • Function Expression: Function expressions can be either named or anonymous. An anonymous function doesn’t have a name, while a named function expression has one. Named function expressions are useful for self-reference within the function.
5. Usage:
   • Function Declaration: Function declarations are typically used for defining functions that you want to be available throughout your entire code, including before and after their declaration.
   • Function Expression: Function expressions are often used when you want to create functions as part of an expression, pass them as arguments to other functions, or limit their scope to a specific block of code.

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In JavaScript, cookies are small pieces of data that websites can store on a user’s computer or device. They are typically used to track and store information about the user’s interactions with a website. Cookies are sent from the web server to the user’s browser and are then stored locally on the user’s device.