What is the purpose of the map method in JavaScript arrays?
- Iterates over each element, allowing you to modify them and returns a new array with the results.
- Removes elements that do not satisfy a certain condition and returns a new array.
- Reduces the array to a single value based on a provided function.
- Returns the first element that satisfies a given condition.
The map method is used to iterate over each element in the array, apply a function to each element, and return a new array with the results. It doesn't modify the original array. This is commonly used for transforming data in arrays.
How does tree shaking contribute to the final bundle size in a JavaScript project?
- Increases the bundle size
- Has no impact on the bundle size
- Decreases the bundle size by removing unused code
- Only affects the bundle size for server-side code
Tree shaking significantly reduces the final bundle size by identifying and excluding unused or dead code. It helps in delivering a more optimized and lightweight application to end-users. Developers can achieve a smaller bundle size, leading to faster load times and improved overall performance, especially in resource-intensive web applications.
In an application dealing with an array of user objects, which higher-order function would be best for filtering users based on specific criteria?
- map
- filter
- reduce
- forEach
The correct option is filter. filter is specifically designed for filtering elements in an array based on a given criteria. It creates a new array with only the elements that satisfy the provided function.
What is the key feature of enhanced object literals in ES6 that allows properties to be set more concisely?
- Shorthand property notation
- Computed property names
- Method shorthand notation
- Default parameter values
In enhanced object literals, shorthand property notation allows concise property assignment. This means you can omit the repetition of the property name if it matches the variable name. This enhances code readability.
What is a potential downside of using higher-order functions excessively in JavaScript?
- Increased complexity and potential for code readability issues
- Improved code maintainability and easier debugging
- Enhanced performance due to optimized function calls
- Reduced flexibility in handling different use cases
Excessive use of higher-order functions can lead to increased code complexity and potential readability issues, as functions become deeply nested and harder to follow.
Is it possible to rename variables while destructuring an object or array?
- Yes, by using the as keyword
- No, renaming is not supported in destructuring
- Yes, by using the rename keyword
- Yes, by providing an alias after a colon
Yes, it is possible to rename variables during destructuring in JavaScript. The as keyword is used to provide an alias for the variable, allowing you to use a different name than the original property or array element.
How do arrow functions behave differently from traditional functions in terms of hoisting?
- Arrow functions are not hoisted
- Arrow functions are hoisted with their entire body
- Arrow functions are hoisted but only the function declaration
- Arrow functions are hoisted with their parameters
Arrow functions are not hoisted, unlike traditional functions. They must be defined before they are used. Option A is correct.
In ES6, what happens when the spread operator is used with an iterable like a string?
- Spreads each character into an array
- Concatenates the string
- Reverses the string
- Throws an error
When the spread operator (...) is used with an iterable like a string, it spreads each character of the string into an array. This allows you to easily convert a string into an array of characters in ES6.
Can generator functions be used to implement asynchronous operations in JavaScript?
- Yes
- No
- Only in modern browsers
- Only in Node.js
Yes, generator functions can be used to implement asynchronous operations using concepts like cooperative multitasking and promises. By yielding promises and handling them appropriately, asynchronous code can be written in a more synchronous style, improving readability and maintainability.
What is the main difference between a mixin and a class in ES6?
- Mixins are Objects
- Classes can have Constructors
- Mixins support Inheritance
- Classes support Composition
The main difference lies in their approach to code structuring. Classes in ES6 follow a classical inheritance model with constructors, while mixins are essentially objects that provide specific functionalities. Mixins promote composition, allowing the combination of features from various sources, while classes are more focused on defining and instantiating objects with a specific structure.
Consider a module that exports multiple utility functions. How would you import a specific function for optimizing bundle size?
- Importing the entire module and using the specific utility function
- Destructuring the import statement to only include the needed utility function
- Importing the module dynamically at runtime based on the required utility function
- Using a wildcard import to import all utility functions
To optimize bundle size, it's advisable to import only the specific utility function needed rather than importing the entire module. Destructuring the import statement allows you to selectively import only the required function, reducing unnecessary code and improving performance.
The ES6 __________ syntax in object literals allows for creating properties with the same name as local variables.
- Rest
- Spread
- Destructuring
- Arrow
In ES6, the destructuring syntax in object literals allows for creating properties with the same name as local variables. It provides a concise way to extract values from objects and arrays.