Hands-On Functional Programming with TypeScript

Laziness

Lazy evaluation is a technique or pattern that delays the evaluation of an expression until its value is needed. We are going to take a look at an example that doesn't use lazy evaluation first so that we can compare it with one that uses lazy evaluation later.

The following code snippet declares an interface named Dog and an array of Dog that contains ten items. The Dog instances have two properties, named size and name. The code snippet also declares two functions, named isLarge and isOld. The isLarge function is used to find the Dog instances, with their size being equal to "L". The isOld function is used to find the Dog instances with an age greater than 5:

interface Dog {   size: "L" | "S";   age: number;   name: string;}const dogs: ...