When a function is defined inside another function and has access to the outer function’s variables, the inner function is known as a _________.
- Nested Function
- Inner Function
- Callback Function
- Closure
A closure is a JavaScript feature where a function has access to variables from its containing (enclosing) function's scope even after the outer function has finished executing. It's a powerful concept for maintaining data privacy and creating functions that remember and can access their outer scope.
What is NOT a consequence of dynamic scoping, considering JavaScript uses lexical scoping?
- Variables can change unexpectedly
- Function definitions capture their context
- Easier to reason about
- Potential bugs due to unexpected changes
In JavaScript, dynamic scoping is not a consequence since JavaScript primarily uses lexical scoping. With lexical scoping, variable scope is determined by the placement of variables in the source code, making it easier to reason about the code's behavior. Dynamic scoping, where scope is determined by the calling context at runtime, can lead to unexpected changes in variable values and potential bugs, but it is not a consequence of JavaScript's lexical scoping.
How can a "for" loop be used for asynchronous operations efficiently?
- By using "await" within the loop body
- By using a "setTimeout" function inside the loop
- By using "return" statements in the loop
- By using "if...else" conditions in the loop
To use a "for" loop for asynchronous operations, you can use the "await" keyword within the loop body, making it an "async" function. This allows you to wait for asynchronous tasks to complete in each iteration, ensuring that the loop proceeds in an orderly fashion. The other options are not suitable for efficient asynchronous operations.
How can you modify the behavior of for...of loops with iterables?
- By using the for...in loop instead.
- By providing a custom iterator object.
- By using Array.prototype.forEach() method.
- By changing the loop syntax (e.g., for...to).
You can modify the behavior of for...of loops with iterables by providing a custom iterator object. Iterables in JavaScript have an @@iterator method that defines how the iteration should behave. By implementing this method, you can customize how for...of iterates over your objects.
Which keyword is used to create a class in JavaScript?
- class
- new
- function
- prototype
In JavaScript, the class keyword is used to create a class. Classes provide a convenient and more structured way to define constructor functions and prototypes. While new is important for instantiating objects, it's not used to create classes. The function and prototype keywords are used in traditional constructor-based object creation.
What method can be used to select the first
element inside a
?
- div.getElementsByTagName('p')[0]
- div.querySelector('p:first-child')
- div.querySelector('p')
- div.getElementByTagName('p')
You can use div.querySelector('p') to select the first
element inside a
. This method finds the first
element that is a descendant of div. Alternatively, you can use getElementsByTagName('p')[0], but querySelector is more flexible and widely used.
How do you declare a variable x and assign it the value 5 in JavaScript?
- var x = 5;
- variable x = 5;
- x = 5;
- let x = 5;
To declare a variable x and assign it the value 5 in JavaScript, you use the syntax var x = 5;. This initializes the variable x with the value 5. You can also use let or const instead of var for variable declaration.
What is the potential issue with using a for...in loop to iterate over arrays?
- It throws an error.
- It iterates only over values.
- It may include inherited properties.
- It can't be used with arrays.
Using a for...in loop to iterate over arrays can lead to a potential issue because it not only iterates over the array's own properties but also includes properties that may be inherited from the prototype chain. This can result in unexpected behavior if you're not careful. To avoid this issue, it's recommended to use for...of loops when iterating over arrays or other iterable objects, as they are designed specifically for this purpose and only iterate over the values of the iterable.
What is the primary role of the setTimeout function in asynchronous JavaScript?
- Delaying code execution
- Executing code repeatedly
- Scheduling tasks
- Controlling the event loop
The primary role of the setTimeout function is to delay the execution of a piece of code for a specified amount of time (in milliseconds). It allows you to schedule a function to run after a specified delay, making it useful for creating timeouts and delays in asynchronous code.
What does the term "scope" refer to in JavaScript?
- The physical size of a webpage
- The lifetime of a variable
- The visibility of a variable
- The security of a webpage
In JavaScript, "scope" refers to the visibility or accessibility of a variable within a specific part of your code. It determines where in your code a particular variable can be used, which helps prevent naming conflicts and maintain code organization.