Beginner Level Questions:
Useful Insights: Highlight the differences between
var has function-level scope, while
const have block-level scope. Also, mention that
const variables cannot be reassigned after declaration.
Useful Insights: Emphasize the distinction between primitive data types (like strings and numbers) and reference data types (like objects and arrays). Discuss the use of the
typeof operator to determine a variable’s data type.
- What is the difference between null and undefined?
Useful Insights: Explain that it’s common for variables to have an initial value of
undefined and that developers can explicitly set a variable to
null when needed.
A for loop is a control structure used to repeat a block of code multiple times. It consists of three parts: the initialization, the condition, and the iteration statement. The loop continues until the condition is false.
Useful Insights: Provide an example of a simple
for loop that counts from 1 to 10. Explain how to use variables to control the loop and how to iterate over arrays using
Intermediate Level Questions:
Useful Insights: Discuss the hierarchical structure of the DOM, with the document as the entry point. Explain how to select elements by ID, class, or tag name and how to manipulate attributes and content.
A closure is a function that has access to variables from its outer (enclosing) function, even after that outer function has finished executing. Closures are commonly used for data encapsulation and creating private variables.
Useful Insights: Provide an example of a closure, like a function that returns another function. Explain how closures capture their lexical scope.
=== are used for equality comparisons.
== performs type coercion, meaning it converts operands to the same type before making the comparison.
=== performs strict (type and value) comparison.
Useful Insights: Discuss how type coercion works with
== and how
=== is often preferred to avoid unexpected results.
Useful Insights: Explain the call stack, callback queue, and message queue components of the event loop. Discuss the concept of non-blocking code and how promises and async/await fit into the event loop.
- What are callbacks, promises, and async/await?
Callbacks are functions passed as arguments to other functions, often used in asynchronous operations. Promises are objects representing the eventual completion (or failure) of an asynchronous operation. Async/await is a modern syntax for handling promises, making asynchronous code more readable and maintainable.
Useful Insights: Provide examples of callback functions, promise chains, and async/await usage. Explain error handling with promises.
Advanced Level Questions:
Useful Insights: Discuss the differences between variable declarations (
var) and variable initializations. Explain that function declarations are fully hoisted, while function expressions are not.
Useful Insights: Explain how objects delegate property and method lookups to their prototypes. Provide examples of creating and extending prototypes using constructor functions and classes.
- What are the differences between function declarations and function expressions?
Function declarations define named functions that are hoisted to the top of their containing scope, allowing them to be called before their actual code appears. Function expressions define functions as values assigned to variables or properties.
Useful Insights: Show examples of both function declarations and function expressions. Discuss their different use cases and how they are hoisted differently.
The this keyword refers to the context within which a function is executed. It can have different values based on how a function is called, such as in a method, a constructor, or a simple function invocation.
Useful Insights: Explain the four common rules for determining the value of
this in a function. Clarify how arrow functions handle
- What is CORS (Cross-Origin Resource Sharing), and how can you enable it on a server?
CORS is a security feature implemented by web browsers to prevent unauthorized web pages from making requests to a different domain. To enable CORS on a server, you need to include specific HTTP headers that allow cross-origin requests.
Useful Insights: Discuss the same-origin policy, the need for CORS, and the HTTP headers used to control it, such as
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