In which scenario might a closure be particularly useful?
- When you want to declare a global variable.
- When you want to protect variables from being modified.
- When you need to maintain access to local variables after the parent function has finished.
- When you want to create a private method in an object.
Closures in JavaScript are particularly useful when you want to create private variables or methods in an object. They allow you to maintain access to local variables even after the parent function has completed its execution. Closures help with data encapsulation and information hiding.
In a Node.js application, you need to perform several database operations consecutively, where each operation depends on the result of the previous one. How might you structure your asynchronous code to handle this scenario efficiently?
- Use Promises and "Promise.all"
- Utilize nested callbacks
- Implement async generators
- Employ event emitters
To efficiently handle consecutive database operations with dependencies in Node.js, you can structure your asynchronous code using Promises and "Promise.all." This approach allows you to create Promises for each operation and then use "Promise.all" to wait for all Promises to resolve. It ensures that operations execute in the correct order and that you can handle dependencies between them easily.
Which method is used to handle the successful resolution of a Promise?
- .then()
- .catch()
- .finally()
- .resolve()
To handle the successful resolution of a Promise, you use the .then() method. This method allows you to specify what should happen once the Promise is fulfilled or successfully resolved. It takes a callback function as its argument, which gets executed when the Promise is resolved.
Imagine you are implementing a feature to upload a file to the server. Which HTTP method would be most appropriate to use with the Fetch API for this purpose?
- GET
- POST
- PUT
- DELETE
To upload a file to the server, you would use the POST HTTP method with the Fetch API. The POST method is used for submitting data to be processed to a specified resource, which is suitable for file uploads. GET, PUT, and DELETE have different purposes.
How to declare a constant array in JavaScript?
- const arr = [];
- const arr = new Array();
- const arr = {}
- const arr = [1, 2, 3];
To declare a constant array in JavaScript, you can use the const keyword followed by square brackets, like const arr = [];. The const keyword ensures that the variable arr cannot be reassigned, making it a constant array.
You are debugging a web page and find that an element isn't being selected as expected with document.querySelector('.example'). What could be a possible reason if the class name is correct?
- Element not present in the DOM
- Element is inside an iframe
- JavaScript not loaded before the query
- Class name contains special characters or spaces
If an element with the correct class name isn't being selected with document.querySelector('.example'), a possible reason could be that the element is not present in the DOM at the time of the query. Ensure that the element you are trying to select exists and is rendered when your JavaScript runs. The other options are less likely causes.
In JavaScript, the _______ method is used to create a new object using an existing object as the prototype of the newly created object.
- Object.create()
- Object.assign()
- Object.extend()
- Object.instantiate()
In JavaScript, the Object.create() method is used to create a new object with the specified prototype object. It allows you to create objects that inherit properties and methods from an existing object, making it a powerful tool for prototypal inheritance.
The switch statement evaluates expressions based on their _________.
- Values
- Cases
- Conditions
- Labels
The switch statement in JavaScript evaluates expressions based on their cases. Each case represents a possible value that the expression can take, and the code block associated with the matching case is executed. This allows for multiple execution paths based on different values of the expression.
When using a for...of loop with strings, each iteration will provide a single _______.
- Character
- Word
- Line
- Number
When using a for...of loop with strings, each iteration will provide a single character. This loop is useful for breaking down strings into individual characters for various processing tasks, such as counting characters or manipulating them individually.
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.