Logical higher-order functions

Up to now, we have been using higher-order functions to produce new results, but there are also some other functions that produce logical results, by applying a predicate to all the elements of an array.

Note

A bit of terminology: the word predicate can be used in several senses (as in Predicate Logic) but for us, in computer science, we adopt the meaning a function that returns true or false. OK, this isn't a very formal definition, but it's enough for our needs. For example, we will filter an array depending on a predicate, and that just means that we get to decide which elements are included or excluded depending on the result of the predicate.

Using these functions implies that your code will become shorter: you can, with a single line of code, get the results corresponding to the whole set of values.

Filtering an array

A common need is having to filter the elements of an array according to some condition. The .filter() method lets you inspect each element of...