JavaScript ES6 Overview

Study Notes: ES6 (Assuming a hypothetical ES6 document exists)

• Introduction to ES6: ES6 (ECMAScript 2015) introduced several significant enhancements to JavaScript, significantly improving syntax, functionality, and developer experience. Key areas impacted include arrow functions, classes, modules and others.

• Arrow Functions:

  • Arrow functions offer a concise syntax for writing function expressions, particularly useful for callback functions.
  • They automatically bind the this value to the enclosing scope.
  • Arrow functions do not have their own this
  • Arrow functions cannot be used as constructors (e.g., new keyword).

• Classes:

  • Introduced in ES6, Classes provide a more structured way to define objects with associated methods.
  • Uses a syntax superficially similar to object-oriented languages.
  • Supports methods (functions within a class) and properties for data members.

• Modules:

  • ES6 modules allow for the organization of JavaScript code into reusable modules.
  • import and export keywords provide for declaration and import.
  • Modules enable better code organization, maintainability, and reusability. The declaration and utilization of modules improves reusability across projects.

• Promises:

  • A primary mechanism for handling asynchronous operations (e.g. AJAX requests, user input).
  • A Promise can be either fulfilled (successful) or rejected (failed).
  • .then, .catch, .finally methods provide robust error handling and execution order.

• Destructuring:

  • A powerful syntax for extracting values from arrays and objects.
  • It allows access to specific object or array parts directly and often improves readability.

• Spread Syntax:

  • Enables copying array or object elements to create new arrays or objects.
  • Useful for manipulating, augmenting, and combining arrays (e.g., adding to an array, or copying existing arrays) or objects.

• Template Literals:

  • Offer a more readable way to define strings with embedded expressions.
  • Use backticks `` instead of double or single quotes for definition.
  • Allows variable embedding within strings in a cleaner way.

• Default Parameters:

  • Functions can be defined with default values for parameters.
  • If a parameter is not provided in a function call, the default value is used.

• Rest Parameters:

  • Functions can accept a variable number of arguments.
  • The ... syntax collects arguments into an array.

(Hypothetical) Possible ES6 Multi-Choice Questions (Illustrative Examples)

• Question 1: Which ES6 feature allows creating reusable code modules?

  • a) Template Literals
  • b) Spread Syntax
  • c) Destructuring
  • d) Modules

• Question 2: How can you write a concise function to handle operations on a variable this in a cleaner way?

  • a) Using the spread operator
  • b) Using ES6 Default Functions
  • c) Arrow functions
  • d) Using ES6 forEach

• Question 3: What will the output of console.log([1,2] + [3,4])

  • a) [4,6]
  • b) "1,23,4"
  • c) Error (Cannot add two arrays with + operator)
  • d) An array of 4 values

• Question 4: What does the import statement do in ES6?

  • a) Exports code from a module for other modules
  • b) Imports code from another module into the current one
  • c) Creates an in-memory copy of code for reuse
  • d) Creates a locally defined constant

• Question 5: What is the correct syntax for a class definition in ES6?

  • a) class MyClass { ... }
  • b) function MyClass() { ... }
  • c) const MyClass = { ... }
  • d) var MyClass = new Object()

• Question 6: What does const arr1 = [1,2,3]; const arr2 = [...arr1,4]; create?

  • a) Creates two identically referenced arrays
  • b) Copies elements from arr1 to arr2 resulting in [1,2,3,4] in arr2
  • c) Modifies arr1 in place.
  • d) Creates a new array arr2 with an unrelated array arr1

• Question 7: Which syntax is used to gather all arguments in a function in ES6?

  • a) param1, param2, ...
  • b) param1, param2, args
  • c) param1, ...args
  • d) ...args

• Question 8: In ES6, what is the most appropriate way to handle asynchronous operations, such as fetching data from a server?

  • a) Callbacks
  • b) Promises
  • c) Async/Await
  • d) Using a global variable.

• Question 9: How do you access properties directly in a destructuring assignment?

  • a) By naming the property in an if statement
  • b) By using the dot operator
  • c) By placing the property name in square brackets
  • d) By assigning the property manually.

• Question 10: What value does the expression undefined?.something; return?

  • a) An error because of the dot notation
  • b) An error because of use of ?
  • c) undefined
  • d) null

(Many more possible questions can be formulated based on the ES6 features, including application-specific syntax examples)