reselect-tree

Wrapper around reactjs's reselect library for creating trees of selectors.

Designed to allow selectors to be organized into separate namespaces easily, with the ability to identify dependencies between selectors in the tree.

Usage Example

Install with:

npm install --save reselect-tree

Then define a file selectors.js:

import { createSelectorTree, createLeaf } from "reselect-tree";

const selectors = require("./dist/reselect-tree.js");
const createSelectorTree = selectors.createSelectorTree;
const createLeaf = selectors.createLeaf;

const select = createSelectorTree({
  shop: {
    taxPercent: state => state.shop.taxPercent
  },
  cart: {
    items: state => state.cart.items,

    subtotal: createLeaf(
      ['./items'],

      (items) => items.reduce((acc, item) => acc + item.value, 0)
    ),

    tax: createLeaf(
      ['/shop/taxPercent', './subtotal'],

      (taxPercent, subtotal) => subtotal * (taxPercent / 100)
    ),

    total: createLeaf(
      ['./subtotal', './tax'], (subtotal, tax) => ({ total: subtotal + tax })
    )
  }
});


let exampleState = {
  shop: {
    taxPercent: 8,
  },
  cart: {
    items: [
      { name: 'apple', value: 1.20 },
      { name: 'orange', value: 0.95 },
    ]
  }
}

console.log(select.cart.subtotal(exampleState)) // 2.15
console.log(select.cart.tax(exampleState))      // 0.172
console.log(select.cart.total(exampleState))    // { total: 2.322 }

You can also select non-leaf nodes, for structured representations:

console.log(select.cart(exampleState))
{ items:
   [ { name: 'apple', value: 1.2 },
     { name: 'orange', value: 0.95 } ],
  subtotal: 2.15,
  tax: 0.172,
  total: { total: 2.322 } }

Override Root Selectors

You can override the default aggregation behavior by defining a custom child _. e.g.:

const select = createSelectorTree({
  shop: {
    taxPercent: state => state.shop.taxPercent
  },
  cart: {
    _: createLeaf(
      ['./items', './total'],

      (items, total) => ({ items, total })
    ),

    items: state => state.cart.items,

    subtotal: createLeaf(
      ['./items'],

      (items) => items.reduce((acc, item) => acc + item.value, 0)
    ),

    tax: createLeaf(
      ['/shop/taxPercent', './subtotal'],

      (taxPercent, subtotal) => subtotal * (taxPercent / 100)
    ),

    total: createLeaf(
      ['./subtotal', './tax'], (subtotal, tax) => ({ total: subtotal + tax })
    )
  }
});

This changes how select.cart behaves, instead acting as select.cart._:

console.log(select.cart(exampleState));   // { items:
                                          //    [ { name: 'apple', value: 1.2 },
                                          //      { name: 'orange', value: 0.95 } ],
                                          //    total: { total: 2.322 } }
console.log(select.cart._(exampleState)); // { items:
                                          //    [ { name: 'apple', value: 1.2 },
                                          //      { name: 'orange', value: 0.95 } ],
                                          //    total: { total: 2.322 } }