How does the "this" keyword behave in event handlers?
- It refers to the element that triggered the event.
- It refers to the document object.
- It always refers to the window object.
- It throws an error since "this" cannot be used in event handlers.
In event handlers, such as those in JavaScript for the web, the "this" keyword typically refers to the DOM element that triggered the event. This behavior allows developers to access and manipulate the specific element that triggered the event, making it a powerful feature in front-end web development.
If you’re building a calculator application using JavaScript, and you want to evaluate operations (+, -, *, /) based on user input, how would you structure a switch statement to handle this?
- Create separate case statements for each operation (+, -, *, /) and perform the corresponding calculation within each case.
- Use regular expressions to match the input against valid operations and handle them accordingly in a single case.
- Convert the user input into a numerical expression and evaluate it within the switch statement.
- Use an if-else statement to check for each operation and perform the corresponding calculation.
To handle different mathematical operations (+, -, *, /) based on user input in a calculator application, it's best to create separate case statements for each operation within a switch statement. This approach is clear and maintainable, allowing you to perform the corresponding calculation for each operation. Using regular expressions within a single case or converting the input into a numerical expression unnecessarily complicates the code. An if-else statement is less idiomatic and less efficient for this purpose.
Which method is commonly used to send data as JSON using Fetch API?
- fetch.post()
- fetch.data()
- fetch.sendJSON()
- fetch()
The fetch() method is commonly used to send data as JSON using the Fetch API. To send JSON data, you can create a request object and use the JSON.stringify() method to convert your data into a JSON string before sending it.
You are asked to create an object that should be instantiated only once and reused in other instances. Which design pattern would you implement?
- Singleton Pattern
- Factory Pattern
- Observer Pattern
- Prototype Pattern
In this scenario, you would implement the Singleton Pattern. The Singleton Pattern ensures that a class has only one instance and provides a global point of access to that instance. It's useful when you need to maintain a single instance of an object that is shared across multiple parts of your application. This can help in scenarios such as creating a global configuration or managing a resource pool.
The main advantage of using arrow functions comes from the lack of a new _________ binding.
- execution context
- lexical scope
- closure
- variable
The main advantage of using arrow functions is that they do not create a new execution context or this binding. Instead, they capture the this value from their surrounding lexical scope. This behavior is known as "lexical scoping," and it provides a predictable way to maintain the value of this in various situations. Thus, the correct option is execution context.
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.