JavaScript: Functional Programming for JavaScript Developers

Filtering streams

As we saw in the preceding section, it is possible to filter a stream of events and, from it produce a new stream of events. You might be familiar with being able to filter items in an array. ES5 introduced a number of new operators for arrays such as filter and some. The first of these produces a new array containing only elements which match the rule in the filter. Some is a similar function which simply returns true if any element of the array matches. These same sorts of functions are also supported on streams as well as functions you might be familiar with from functional languages such as First and Last. In addition to the functions which would make sense for arrays, there are a number of time series based functions which ...