Chapter 5. Programming Declaratively - A Better Style

Up to now, we haven't really been able to appreciate the possibilities of FP, as pertains to working at a higher level, declarative fashion. In this chapter, we will correct that, and start getting shorter, more concise, and easier to understand code, by using some higher-order functions (HOF: functions that take functions as parameters) such as:

• .reduce() and .reduceRight() to apply an operation to a whole array reducing it to a single result
• .map(), to transform an array into another, by applying a function to each of its elements
• .forEach(), to simplify writing loops, by abstracting the necessary looping code

We'll also be able to do searches and selections with:

• .filter(), to pick some elements from an array
• .find() and .findIndex(), to search for elements satisfying a condition
• And a pair of predicates, .every() and .some(), to check an array for some Boolean test

Using these functions lets you work more declaratively, and you'll see that...