In a web application that requires real-time data updates, how would the choice between Promises and callbacks affect performance and user experience?
- Promises may offer better performance due to their asynchronous nature
- Callbacks are preferable for real-time updates
- There's no significant impact on performance or user experience
- Promises introduce delays in real-time updates
In a web application requiring real-time data updates, choosing Promises may lead to better performance. Promises operate asynchronously, allowing non-blocking execution and potentially improving responsiveness. Callbacks, on the other hand, might result in callback hell and may not provide the same level of performance as Promises in handling real-time updates.
When using fetch, convert the response to JSON inside a try block and handle errors in ________.
- catch block
- then block
- finally block
- parse block
When fetching data with the 'fetch' API, it's advisable to convert the response to JSON inside a try block to handle successful responses and catch block to handle errors.
How does a for...of loop differ from a for...in loop in terms of iteration?
- for...of is used for arrays and iterable objects
- for...in is used for arrays and iterable objects
- for...of iterates over property values
- for...in iterates over property names
The for...of loop is designed specifically for iterating over values of iterable objects, such as arrays, while the for...in loop iterates over property names and is not limited to iterable objects.
In a scenario where an application needs to make several API calls and only proceed after all have successfully completed, what Promise method would be most appropriate?
- Promise.race
- Promise.all
- Promise.resolve
- Promise.reject
When dealing with multiple asynchronous operations, Promise.all is used to wait for all promises to be resolved. It ensures that the application proceeds only when all the promises are successfully completed, making it suitable for scenarios where multiple API calls need to be made concurrently.
What is the correct syntax to create an instance of a class in ES6?
- let obj = new Class();
- let obj = create(Class);
- let obj = Object.create(Class);
- let obj = Class.create();
The correct syntax to create an instance of a class in ES6 is to use the new keyword followed by the class name and parentheses, like this: let obj = new Class();. The new keyword is essential for creating instances and invoking the class constructor.
Can a default export be imported with any name?
- Yes
- No
- Only in certain cases
- Depends on the file structure
In ES6, a default export can be imported with any name. The imported name is not dictated by the exporting module. It allows flexibility in naming while importing, making it more convenient.
When using Symbols for object properties, they are not included in __________ enumerations.
- for...in'
- forEach'
- Object.keys()'
- Object.getOwnPropertySymbols()'
Object properties with Symbols as keys are not included in for...in enumerations. To get all property keys (including Symbols), you can use Object.getOwnPropertySymbols() in addition to other methods. Example: const symbols = Object.getOwnPropertySymbols(myObject);
Destructuring an object within a _________ allows for directly mapping object properties to function parameters.
- Callback function
- Template literal
- Arrow function
- Promise
Destructuring an object within an "Arrow function" allows for directly mapping object properties to function parameters. Arrow functions provide a concise syntax, and when combined with destructuring, you can streamline the mapping of object properties to function parameters.
To check if a Map contains a certain key, use the _________ method.
- hasKey
- checkKey
- has
- includes
The correct method is has. In JavaScript, the Map object has a has method that returns a boolean indicating whether the map contains a specified key. Example: myMap.has('key').
How does chaining array methods like map and filter affect performance?
- Negatively impacts performance due to multiple iterations
- Positively impacts performance by optimizing the code
- No significant impact on performance
- Only affects readability, not performance
Chaining array methods like map and filter can negatively impact performance due to multiple iterations. Each method creates a new array, and chaining them leads to intermediate arrays, causing additional iterations. This can be inefficient, especially for large datasets.