Practical Modern JavaScript

Chapter 9. Practical Considerations

JavaScript is an ever-evolving language. Its development rhythm has had different paces throughout the years, entering a high-velocity phase with the introduction of ES5. Thus far, this book has taught you about dozens of language features and syntax changes introduced in ES6, and a few that came out afterwards, in ES2016 and ES2017.

Reconciling all of these new features with our existing ES5 knowledge may seem like a daunting task: what features should we take advantage of, and how? This chapter aims to rationalize the choices we have to make when considering whether to use specific ES6 features.

We’ll take a look at a few different features, the use cases where they shine, and the situations where we might be better off using features that were already available in the language. Let’s go case by case.

9.1 Variable Declarations

When developing software, most of our time is spent reading code, instead of writing it. ES6 offers let and const as new flavors of variable declaration, and part of the value in these statements is that they can signal how a variable is used. When reading a piece of code, others can take cues from these signals in order to better understand what we did. Cues like these are crucial to reducing the amount of time someone spends interpreting what a piece of code does, and as such we should try and leverage them whenever possible.

A let statement indicates that a variable can’t be used before its declaration, due to the ...