What is a closure in JavaScript?
- A secure way to store passwords
- A private function
- A way to handle exceptions
- A function that remembers its lexical scope
A closure in JavaScript is a function that "remembers" its lexical scope, even when it's executed outside that scope. This allows the function to maintain access to variables from its parent scope, creating a powerful mechanism for encapsulation and data privacy.
In which context does the "this" keyword not refer to the object that calls the function?
- Global context
- Method context
- Function context
- Constructor context
The "this" keyword in JavaScript does not refer to the object that calls the function in the global context. In the global context, "this" points to the global object, which is usually the "window" object in browsers. This can be a source of confusion, so it's essential to understand the various contexts in which "this" behaves differently.
Why might recursive function expressions cause issues in certain scenarios?
- They can cause an infinite loop and lead to a stack overflow error.
- They can only be used for mathematical calculations and not for general-purpose recursion.
- They can't access variables from the outer scope.
- They are less efficient than iterative approaches.
Recursive function expressions, if not designed carefully, can cause infinite recursion, which leads to a stack overflow error. Each recursive call adds a new function call to the stack, and if there's no base case to stop the recursion, it will continue indefinitely. It's essential to have a termination condition to prevent such issues.
To handle both resolve and reject in a single method, you can use the .finally method after a(n) _______ block in asynchronous functions.
- try
- await
- then
- catch
To handle both resolve and reject outcomes in a single method, you can use the .finally() method after a try block in asynchronous functions. This ensures that the provided code block is executed regardless of whether the Promise is resolved or rejected.
Which method removes the last element from an array and returns that element?
- shift()
- pop()
- unshift()
- splice()
The pop() method in JavaScript is used to remove the last element from an array and return that element. This is commonly used for tasks like removing the last item from a stack implemented as an array. shift() removes the first element, unshift() adds elements to the beginning, and splice() is used for more complex array manipulation.
The ______ operator is used to check both value and type.
- ==
- ===
- =
- !==
The === operator in JavaScript is used for strict equality comparison. It checks both the value and the type of the operands. It returns true if both the value and the type are the same, and false otherwise. Understanding strict equality is crucial to prevent unexpected type coercion bugs.
What will be the return value of ["apple", "banana", "cherry"].pop();?
- "apple"
- "banana"
- "cherry"
- undefined
The return value will be "cherry". The pop() method removes the last element from an array and returns that element. In this case, it removes "cherry" from the end of the array and returns it.
What is the primary use of a "for" loop in JavaScript?
- Iterating over an array
- Defining a variable
- Printing to the console
- Adding new elements to an object
The primary use of a "for" loop in JavaScript is to iterate over an array or any iterable data structure. It allows you to repeatedly execute a block of code for each item in the iterable, making it a powerful tool for tasks like data processing, manipulation, and rendering in web applications. "for" loops are not typically used for defining variables, printing to the console, or adding new elements to an object.
While developing a web application, you create a class "Product" to hold the basic attributes of products in an e-commerce site. Later, you need to extend the functionality of some products which are on sale without altering the "Product" class. Which design pattern might be most appropriate to implement this additional functionality without modifying the existing "Product" class?
- Decorator Pattern
- Factory Method Pattern
- Singleton Pattern
- Observer Pattern
The Decorator Pattern is a suitable choice in this scenario. It allows you to add new behaviors or functionality (e.g., for products on sale) to existing classes (e.g., "Product") without modifying their structure. This ensures the open-closed principle and maintainability.
To iterate over the keys in an object, you can use the for...______ loop.
- For...Of
- For...In
- For...Each
- For...While
To iterate over the keys in an object, you can use the for...In loop. This loop is specifically designed for iterating over object properties, allowing you to access each key. The for...Of loop, on the other hand, is used for iterating over the values of iterable objects like arrays.
What is the most common issue developers might face when working with closures and loops together?
- Variable hoisting
- Memory leaks
- Unexpected type coercion
- Event propagation
The most common issue when working with closures and loops together is the creation of memory leaks. This happens when closures inside loops capture references to variables that are continuously changing in the loop, preventing them from being garbage collected, and leading to increased memory consumption. It's crucial to understand and manage these cases to avoid performance problems.
In a while loop, placing a ________ statement inside the loop can help prevent infinite loops by providing an explicit exit.
- Break
- Continue
- Return
- Stop
In a while loop, placing a "break" statement inside the loop can help prevent infinite loops by providing an explicit exit condition. When a certain condition is met, the "break" statement terminates the loop, allowing you to exit the loop when necessary and avoid infinite iterations.