Functional data structures in JavaScript with Mori by Jesse Hallett.
From the post:
I have a long-standing desire for a JavaScript library that provides good implementations of functional data structures. Recently I found Mori, and I think that it may be just the library that I have been looking for. Mori packages data structures from the Clojure standard library for use in JavaScript code.
Functional Data Structures
A functional data structure (also called a persistent data structure) has two important qualities: it is immutable and it can be updated by creating a copy with modifications (copy-on-write). Creating copies should be nearly as cheap as modifying a comparable mutable data structure in place. This is achieved with structural sharing: pointers to unchanged portions of a structure are shared between copies so that memory need only be allocated for changed portions of the data structure.
A simple example is a linked list. A linked list is an object, specifically a list node, with a value and a pointer to the next list node, which points to the next list node. (Eventually you get to the end of the list where there is a node that points to the empty list.) Prepending an element to the front of such a list is a constant-time operation: you just create a new list element with a pointer to the start of the existing list. When lists are immutable there is no need to actually copy the original list. Removing an element from the front of a list is also a constant-time operation: you just return a pointer to the second element of the list….
Just in case you want to start practicing your functional programming in JavaScript.
I first saw this in Christophe Lalanne’s Bag of Tweets for November 2013.