Add pick to frptools. Document all utility functions

README.md

@@ -228,3 +228,28 @@ node to use to propagate updates but firing other values could have some uses.
 const unsubscribe = inViewport.subscribe(console.log.bind(console));
 inViewport.fire(false); // "false" logged to console.
 ```
+
+# Utilities
+
+## id
+
+`id(anything) -> anything`
+
+`id` is a function that returns its first parameter. It is used as the default hash function for
+each subscribable.
+
+## call
+
+`call(anything) -> void`
+
+`call` will call the first parameter if it is a function. It is used for iterating over
+subscribables.
+
+## pick
+
+`pick(propName, default) -> (obj) -> any`
+
+`pick` returns a function that accepts an object and will return the object's property for the
+provided name or the default if one is supplied. `pick` is not directly used with any subscribable
+but can be useful as the computed function when breaking down a `prop` that contains an object or a
+container.

package.json

@@ -1,6 +1,6 @@
 {
 	"name": "frptools",
-	"version": "3.0.0",
+	"version": "3.0.1",
 	"description": "Observable Property and Computed data streams",
 	"main": "lib/index.js",
 	"jsnext:main": "src/index.js",

src/index.js

@@ -1,4 +1,4 @@
 export { prop } from './property';
 export { computed } from './computed';
 export { container } from './container';
-export { call, id } from './util.js';
+export { call, id, pick } from './util.js';

src/util.js

@@ -1,5 +1,11 @@
 export const id = a => a;
 
+export const pick = (id, def) => doc => (doc && doc.hasOwnProperty(id) ? doc[id] : def);
+
+export const call = a => (typeof a === 'function' ? a() : a);
+
+// internal utilities
+
 export const registerSubscriptions = subscriptionsArray => fn => {
 	subscriptionsArray.push(fn);
 	return () => {
@@ -11,8 +17,6 @@ export const registerSubscriptions = subscriptionsArray => fn => {
 	};
 };
 
-export const call = a => (typeof a === 'function' ? a() : a);
-
 export const registerFire = subscriptionsArray => val => {
 	subscriptionsArray.map(s => s(val)).forEach(call);
 };