Hands-On Functional Programming with TypeScript

Static variables powered by closures

In the previous section, we learned that, when a variable in a closure context can be shared between multiple instances of a class, this means that the variable behaves like a static variable. We will now see how we can create variables and methods that behave like a static variable using closures. Let's start by declaring a TypeScript class named Counter:

class Counter { private static _COUNTER = 0; public increment() { this._changeBy(1); } public decrement() { this._changeBy(-1); } public value() { return Counter._COUNTER; } private _changeBy(val: number) { Counter._COUNTER += val; }}

Please note that the preceding example is meant to be a TypeScript example.

The preceding class contains a static member ...