You Don't Know JS: ES6 & Beyond

Chapter 5. Collections

Structured collection and access to data is a critical component of just about any JS program. From the beginning of the language up to this point, the array and the object have been our primary mechanism for creating data structures. Of course, many higher-level data structures have been built on top of these, as user-land libraries.

As of ES6, some of the most useful (and performance-optimizing!) data structure abstractions have been added as native components of the language.

We’ll start this chapter first by looking at TypedArrays, which were technically contemporary to ES5 efforts several years ago, but only standardized as companions to WebGL and not JavaScript itself. As of ES6, these have been adopted directly by the language specification, which gives them first-class status.

Maps are like objects (key/value pairs), but instead of just a string for the key, you can use any value—even another object or map! Sets are similar to arrays (lists of values), but the values are unique; if you add a duplicate, it’s ignored. There are also weak (in relation to memory/garbage collection) counterparts: WeakMap and WeakSet.

TypedArrays

As we cover in the Types & Grammar title of this series, JS does have a set of built-in types, like number and string. It’d be tempting to look at a feature named “typed array” and assume it means an array of a specific type of values, like an array of only strings.

However, typed arrays are really more about providing structured ...