Before diving into design patterns in JavaScript, it's crucial to understand the fundamentals of JavaScript and the features introduced in ECMAScript 6 (ES6). This chapter serves as a refresher to ensure we're all on the same page.

Variables and Scope

JavaScript allows declaring variables using var, let, and const.

• var has function scope and can be redeclared.
• let has block scope and cannot be redeclared in the same scope.
• const is similar to let, but in addition to being block-scoped, it creates a constant that cannot be reassigned.

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Arrow Functions

Arrow functions provide a more compact syntax for writing functions. Additionally, they do not have their own this context, which can be useful in certain cases.

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Classes and Inheritance

ES6 introduced class syntax, making it easier to create objects and handle inheritance.

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Destructuring

Destructuring allows you to extract values from arrays or objects and assign them to variables.

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Default Parameters and Rest/Spread

We can assign default values to function parameters and use the rest/spread operator to handle multiple arguments.

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Promises and Async/Await

Promises are essential for handling asynchronous operations in JavaScript. ES8 introduced async and await, which simplify working with promises.

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To understand and effectively apply design patterns, it's fundamental to be comfortable with these modern JavaScript features.