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.
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.
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.
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.
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.
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.
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.
You're developing a Node.js application and notice that the "this" keyword inside a regular function, defined in the global scope, refers to something different than you're used to in client-side JavaScript. What does "this" refer to in this context?
- It refers to the Node.js global object (e.g., "global" or "window")
- It refers to the "exports" object
- It refers to the "module.exports" object
- It refers to the function itself
In Node.js, when you define a regular function in the global scope (outside any function or module), "this" inside that function refers to the Node.js global object (e.g., "global" in Node.js or "window" in the browser). This behavior is different from client-side JavaScript, where "this" in the global scope refers to the global window object.
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.
Can a function expression be used before it is defined in the code?
- No, function expressions can only be used after their definition.
- Yes, function expressions are hoisted and can be used before they are defined.
- It depends on whether the function expression is named or anonymous.
- No, function expressions are not valid in JavaScript.
Function expressions are not hoisted in JavaScript, which means they can only be used after they are defined in the code. Attempting to use a function expression before its declaration will result in an error. This is different from function declarations, which are hoisted and can be used before their declaration. It's essential to understand this behavior to avoid bugs and unexpected behavior in your JavaScript programs.