Javascript Interview Questions For 3 Years Experience
3 Years Experienced? Crush These Javascript Interview Qs in Style!
JavaScript is a widely used and popular programming language, especially in the field of web development. With the increasing demand for skilled JavaScript developers, it is important for candidates with 3 years of experience to have a strong understanding of this language. In an interview for a JavaScript position, one can expect questions related to basic concepts, such as data types, functions, and objects, as well as more advanced topics, such as closures, event handling, and AJAX. Employers may also ask for examples of projects that candidates have worked on and their problem-solving approach. Additionally, having knowledge of popular libraries and frameworks like Angular, React, and jQuery can also be beneficial. Being well-prepared and confident in answering technical and scenario-based questions can greatly increase the chances of success in a JavaScript interview.
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1 - What is hoisting in JavaScript?
Hoisting is a JavaScript concept that allows variables and function declarations to be moved to the top of their scope before code execution. This means that even if a variable or function is declared after it is used, it will still be accessible. However, only the declaration is hoisted, not the assignment.
2) What is closure in JavaScript?
Closure is a feature in JavaScript that allows inner functions to have access to variables defined in their outer function, even after the outer function has returned. This helps with encapsulation and allows for private variables and functions in JavaScript.
3) What is a JavaScript event loop?
The event loop is a mechanism in JavaScript that allows for the execution of asynchronous code. It continuously checks the call stack and the task queue for any tasks that need to be executed, prioritizing the call stack first. This is what allows JavaScript to handle multiple tasks concurrently.
4) What is the difference between let, var, and const?
let and var are used for variable declaration, while const is used for constant declaration. The main difference between let and var is that let has block scope, meaning it is only accessible within the block it is declared in, while var has function scope, meaning it is accessible throughout the function it is declared in.
5) How is prototypal inheritance implemented in JavaScript?
Prototypal inheritance is implemented through the prototype chain. Every object in JavaScript has a prototype property, which refers to the object it inherited from. If a property or method is not found in an object, JavaScript checks the prototype object, and if it's still not found, it continues up the chain until it reaches the Object prototype.
6) Explain JavaScript events and event bubbling?
Events in JavaScript are actions that occur in the DOM, such as a click or keypress. Event bubbling is a concept where when an event occurs on an element, the event is propagated upwards through its parent elements. This allows for event handlers to be triggered on multiple elements without attaching them to each individual element.
7) What is the difference between == and === in JavaScript?
The double equals (==) is a loose equality operator, meaning it attempts to convert the values being compared to the same type before making the comparison. The triple equals (===) is a strict equality operatomeaning it does not attempt to convert the values and will only return true if both values ahe same type and have the same value.
8) What is the difference between null and undefined in JavaScript?
Null represents an intentional absence of any value, while undefined represents a variable or object property that has not been assigned a value. In other words, null is usually explicitly set by a programmer, while undefined is the default value assigned to a variable.
9) Describe the difference between synchronous and asynchronous code in JavaScript?
Synchronous code is executed sequentially, meaning each line of code is executed in order and the next line will not be executed until the previous one has finished. Asynchronous code, on the other hand, allows for multiple tasks to be performed at the same time, with the result of one task not affecting the execution of another.
10) Explain the keyword ‘this’ in JavaScript?
The ‘this’ keyword in JavaScript refers to the object that is currently being operated on. Its value depends on the context in which it is used. In global scope, ‘this’ refers to the global object (window in the browser). In a function, ‘this’ refers to the object that contains the function. In an event handler, ‘this’ refers to the element that triggered the event.
11) How can you optimize your website for better performance?
There are several ways to optimize website performance, such as using minification to reduce file sizes, optimizing images and using lazy loading, reducing HTTP requests, leveraging browser caching, and implementing a content delivery network (CDN).
12) What is the difference between a for loop and a for in loop in JavaScript?
A for loop is used to iterate over a given number of times, while a for in loop is used to iterate over the properties of an object. The for loop typically uses a counter variable and a condition for termination, while a for in loop uses the ‘in’ keyword to loop through an object's properties.
13) How do you determine the type of a variable in JavaScript?
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The typeof operator can be used to determine the type of a variable or value in JavaScript. It returns a string indicating the type of the operand.
14) What is a JavaScript promise?
A promise is an object that represents the eventual completion or failure of an asynchronous operation. It allows for cleaner and easier handling of asynchronous code as it uses a chainable API to handle success and error callbacks.
15) How can you handle errors in JavaScript?
Errors in JavaScript can be handled by using the try catch statement. The code that is likely to throw an error is wrapped in the try block, and the catch block is used to handle the error if it occurs. Additionally, the finally block can be used to execute code regardless of the outcome of the try block.
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