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Section 5 – Important JavaScript concepts and syntax
These are bonus chapters available online for readers who want to understand JavaScript at a deeper level.
Chapter 19, Important Concepts in JavaScript, provides a comprehensive primer on the most fundamental (and most overlooked) principles of JavaScript, including data types, prototypes, the prototype inheritance chain, ES6 classes, this, context, and the execution context.
https://www.packtpub.com/sites/default/files/downloads/ImportantConceptsinJavaScript.pdf
Chapter 20, Writing in ECMAScript 2015+, guides you through the newer features of JavaScript, such as let/const, defaults, destructuring assignment, rest and spread operators, template literals, and promises.
https://www.packtpub.com/sites/default/files/downloads/WritinginECMAScript2015.pdf