How would you use mixins in ES6 to enhance classes in a library, without modifying the original source code?

  • By directly modifying the source code of the original class.
  • By creating a new class that extends the original class and includes the desired mixins.
  • By using decorators to dynamically apply mixins to the original class.
  • By creating a higher-order function that adds mixins to the original class prototype.
To enhance classes in a library without modifying the source code, you can create a new class that extends the original class and includes the desired mixins. This follows the concept of class extension and composition.

What happens if super() is called multiple times in a constructor?

  • It triggers an error
  • It executes the parent constructor multiple times
  • Only the last call is effective
  • It has no effect
Calling super() multiple times in a constructor is an error. It must be called once and must be the first statement in the constructor. Subsequent calls to super() would result in an error.

What is the main purpose of default parameters in ES6 functions?

  • Enhancing Function Flexibility
  • Enabling Type Annotations
  • Facilitating Function Overloading
  • Simplifying Function Parameter Handling
Default parameters in ES6 functions provide a way to set default values for function parameters, enhancing flexibility by allowing functions to be called with fewer arguments or without any arguments. This can simplify code and handle different use cases without requiring explicit checks for undefined values.

The _________ method is used to execute a function on each item in a Set.

  • forEach
  • execute
  • loop
  • iterate
The correct method is forEach. The forEach method in Set allows you to execute a provided function once for each element in the Set, in insertion order. Example: mySet.forEach((value) => console.log(value));.

Using a WeakMap for private data ensures that the data is garbage collected when the object key is no longer ________.

  • Referenced
  • Immutable
  • Mutable
  • Valid
When using a WeakMap for private data, the data is tied to the object key, and it will be garbage collected when the object is no longer referenced elsewhere in the code. This helps in managing memory efficiently for private data in JavaScript.

In a scenario where a function needs to access the this keyword of a containing object, should an arrow function be used?

  • Yes, always
  • No, never
  • It depends
  • Only in classes
Arrow functions should not be used in this scenario because they do not bind their own "this" and instead inherit it from the enclosing scope. This can lead to unintended behavior when trying to access the "this" keyword of a containing object.

In a scenario where a function receives a complex object as an argument, how can destructuring assignment enhance code readability and maintenance?

  • It has no effect on code readability
  • It makes code more complex
  • It simplifies the extraction of values from the object
  • It can only be used with primitive data types
When a function receives a complex object as an argument, using destructuring assignment can significantly enhance code readability and maintenance. By specifying the necessary properties directly in the function parameter, developers can easily understand which values the function expects. This not only simplifies the code but also reduces the need for repeated object property access, making the code more efficient and easier to maintain.

Consider a scenario where you are handling multiple independent API calls. How would the approach differ using Promises compared to callbacks?

  • Promises allow for better parallel execution
  • Callbacks are more suitable for independent calls
  • Promises are slower for independent calls
  • Callbacks lead to callback hell
When dealing with multiple independent API calls, Promises offer a significant advantage by allowing for better parallel execution. Unlike callbacks, which may result in nested structures (callback hell), Promises provide a more elegant solution through chaining, resulting in cleaner and more maintainable code.

Consider a function designed to format a date. How would you use default parameters to provide flexibility in the format?

  • Utilize default parameters to allow users to specify the format, such as formatDate(date, format = "YYYY-MM-DD").
  • Use default parameters for individual components like day, month, and year, enabling customization while maintaining a default format.
  • Allow a default format but also accept an optional format parameter, giving users the ability to override the default if needed.
  • Use default parameters to set a default format but allow users to pass a custom formatting function, giving maximum flexibility.
Default parameters in JavaScript allow you to assign default values to function parameters. In the context of formatting a date, default parameters can be used to provide a default format, and users can override this by passing their desired format as an argument. This provides a balance between having a predefined format and allowing customization based on user needs.

What is the outcome of trying to mutate the properties of an object declared with const?

  • Mutation is allowed
  • Mutation is not allowed
  • Mutation is allowed, but with restrictions
  • Mutation is allowed only for primitive properties
When an object is declared with const, its reference cannot be reassigned, but the properties can be mutated. It's important to note that const protects the reference, not the content. So, attempting to reassign the entire object will result in an error, but modifying its properties is permissible.