What is the purpose of the "else" statement in JavaScript?
- To specify an alternate code block to execute when the condition is false
- To terminate the program
- To define a variable
- To loop through an array
The "else" statement in JavaScript serves the purpose of specifying an alternate code block to execute when the condition specified in the "if" statement is false. It provides an alternative path for your code's execution.
What is a key difference between arrow functions and regular functions in JavaScript?
- Arrow functions have their own 'this' context
- Regular functions are more concise
- Arrow functions cannot have parameters
- Regular functions do not allow for anonymous functions
One significant difference between arrow functions and regular functions is that arrow functions do not have their own 'this' context; instead, they inherit 'this' from the surrounding code. Regular functions, on the other hand, have their own 'this' context, which can vary depending on how the function is called.
How does the "this" keyword behave in arrow functions compared to regular functions?
- It refers to the global object.
- It retains the value of "this" from its enclosing lexical context.
- It becomes undefined.
- It refers to the parent function's "this".
In arrow functions, the value of "this" is determined by its enclosing lexical context (the function that contains it). This behavior is different from regular functions, where "this" is dynamically scoped and can change based on how the function is called. This makes arrow functions particularly useful for maintaining the expected value of "this" in functions defined within methods or callbacks.
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.
What is the significant difference between Java and JavaScript?
- Java is primarily a client-side language
- JavaScript is a compiled language
- Java is a strongly typed language
- JavaScript is primarily used for web scripting
The significant difference between Java and JavaScript lies in their purpose and usage. Java is primarily a server-side language, whereas JavaScript is used for client-side web scripting. Additionally, Java is a statically typed language, while JavaScript is dynamically typed, which means variable types are determined at runtime. Understanding these differences is essential when choosing the right language for a particular task.