Javascript Programming Interview Questions

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Javascript Programming Interview Questions

Expertly Crafted JavaScript Programming Interview Questions

JavaScript is a popular programming language used for creating dynamic and interactive web pages. In a programming job interview, candidates may be asked various questions related to JavaScript to assess their understanding of the language, its syntax, and its functionality. These questions may cover topics such as data types, control structures, functions, events, DOM manipulation, and more. Employers may also ask candidates about their experience with debugging and problem-solving in JavaScript, as well as their knowledge of popular frameworks like React and Angular. The purpose of these questions is to evaluate a candidate's proficiency in JavaScript and their ability to write efficient and error-free code.

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1 - What is the difference between null and undefined?

Null is an explicitly assigned value that means there is no value present. Undefined, on the other hand, means that a variable or property has been declared, but no value has been assigned to it. Essentially, null means the absence of a value, while undefined means the absence of a defined value.

2) What is the difference between == and === in JavaScript?

The == operator checks for equality in value, while the === operator checks for equality in both value and data type. This means that the === operator is more strict, as it will only return true if both operands are of the same data type.

3) What is a closure in JavaScript?

A closure is a function that has access to variables in its outer scope, even after the outer function has returned. This allows for data privacy and helps to avoid conflicts with other variables in the global scope.

4) What is the difference between let, var, and const in JavaScript?

Let and var are used for variable declaration, but the main difference is that let is block scoped, while var is function scoped. Const, on the other hand, is used for constants that cannot be reassigned.

5) What is event bubbling and event capturing in JavaScript?

Event bubbling is the process where an event is triggered on an element and then bubbles up through all of its parent elements. Event capturing is the opposite, where the event is triggered at the topmost parent element and then propagates down to the selected element.

6) What is the difference between synchronous and asynchronous programming in JavaScript?

Synchronous programming refers to code that is executed in a single thread, where one line of code is executed at a time before moving onto the next one. Asynchronous programming allows multiple tasks to be executed simultaneously, improving the performance of the code.

7) What is a callback function in JavaScript?

A callback function is a function that is passed as an argument to another function and is executed once the first function has completed its task. This allows for better control over the flow of the code and can be useful for handling asynchronous tasks.

8) What is the use of the “this” keyword in JavaScript?

The “this” keyword refers to the current context in which a function is executed. It can be used to access and manipulate properties and methods within an object, as well as bind functions to different objects.

9) What are the different data types in JavaScript?

JavaScript supports several data types, including string, number, boolean, null, undefined, symbol, and object. It is a dynamic language, meaning that data types can change at runtime.

10) How do you handle errors in JavaScript?

Errors in JavaScript can be handled using try/catch blocks, where the code within the try block is executed, and any errors are caught and handled in the catch block. This helps to avoid abrupt crashes and allows for cleaner and more efficient code.

11) What is a prototype in JavaScript?

A prototype is an object that is used as a blueprint for creating new objects. It provides a set of properties and methods that can be inherited by the new objects, helping to save memory and improve code efficiency.

12) How can you debug JavaScript code?

The most common way to debug JavaScript code is by using the console.log() method, which prints messages to the browser console. Other methods include using breakpoints in the browser's built in developer tools or using a JavaScript debugger.

13) What are arrow functions in JavaScript?

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Arrow functions are a shorthand syntax for writing functions in JavaScript. They use the => (fat arrow) notation and have a more concise syntax compared to traditional functions. They also have the added benefit of having the “this” keyword bound to the outer scope.

14) What is hoisting in JavaScript?

Hoisting is a mechanism in JavaScript where variable declarations are moved to the top of their scope. This allows variables to be used before they are declared, but can also lead to unexpected results if not properly understood.

15) What is the difference between let and const in JavaScript?

Both let and const are used for variable declaration, but the main difference is that let variables can be reassigned, while const variables cannot. This makes const more suitable for constants that should not be changed.


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