Programming Declaratively – A Better Style

Up to now, we haven’t really been able to appreciate the possibilities of functional programming (FP) as it pertains to working in a higher-level, declarative fashion. In this chapter, we will correct this and start producing shorter, more concise, and easier-to-understand code, by using some higher-order functions (HOFs) —that is, functions that take functions as parameters, such as the following:

• reduce() and reduceRight() to apply an operation to a whole array, reducing it to a single result
• map() to transform one array into another by applying a function to each of its elements
• flat() to make a single array out of an array of arrays
• flatMap() to mix together mapping and flattening
• forEach() to simplify writing loops by abstracting the necessary looping code

We’ll also be able to perform searches and selections with the following:

• filter() to pick some elements from an array...