kontext

A higher-order function that proxies context to context free functions.

Install

$ yarn install kontext

Usage

Provide context values to context-free functions.

import kontext from 'kontext';
import { compose, log, prop, } from './util';

// define a generic function
const greet = compose(
  log,
  prop(`greeting`),
);

// define a context
function Greeter(opts = {}) {
  this.greeting = opts.greeting;
}
// lift the generic function into the context
Greeter.prototype.greet = kontext([ `greeting`, ])(greet);

const dog = new Greeter({
  greeting: `Hello. This is Dog.`,
});
dog.greet(); // 'Hello. This is Dog.'

Compose context-free functions with a context setter to mutate the context.

import kontext from 'kontext';
import { add, compose, } from './util';

const count = prop(`count`);
const setCount = (count) => ({ count, });
const withCount = kontext([ `count`, ]);

function Counter(opts = {}) {
  this.count = opts.init || 0;
}

// compose generic functions with the context setter to mutate the context
const inc = (ctx, setCtx) => compose(
  setCtx,
  setCount,
  add(1),
  count,
)(ctx);
Counter.prototype.inc = withCount(inc);

// create reusable logic that isn't coupled to `this`.
const skip = (n, ctx, setCtx) => compose(
  setCtx,
  setCount,
  add(n),
  count,
)(ctx);
Counter.prototype.skip = withCount(skip);

const counter = new Counter({ init: 1, });
counter.count; // 1
counter.inc();
counter.count; // 2
counter.skip(10);
counter.count; // 12

API

kontext(ctxKeys)(baseFunction)

Takes an array of keys and returns a higher-order function. Picks each key from the context and provides the result to the base function.

ctxKeys

Type: Array k

An array of keys to pick from the function context.

baseFunction(...*, ctx, setCtx)

The function to lift into the context. The higher-order function appends ctx and setCtx to the arguments list of baseFunction.

ctx

Type: {k: *}

The result of picking ctxKeys from the function context. The ctx object is a collection of key/value pairs. Each key is an item in the ctxKeys array. Each value is the value of that key on the function's context. The value of a key that is not found on the function context is undefined on the ctx object. kontext binds function values to the context.

setCtx(props)

Type: ({k: *}) -> {k: *}

Updates the context with each of the provided key/value pairs. The values of existing keys are overwritten. Any key in props which refers to an inherited property will become an own property when updated with setCtx.

props

Type: {k: *}

A collection of key/value pairs where each key is a context property to update and each value is the new value of that property.

License

MIT © Max Hallinan