selectorator

selectorator is an abstraction API for creating selectors via reselect with less boilerplate code.

Table of contents

• Installation
• Versions
• Usage
  • Shorthand types
  • TypeScript
• Options
  • deepEqual
  • isEqual
  • memoizer
  • memoizerOptions
• Development

Installation

$ npm i selectorator --save

Versions

Versions of selectorator on or above 3.x.x will use the corresponding major version of reselect as a dependency. If you wish to still use the 2.x.x branch of reselect for your application, then you should continue using the 1.x.x branch of selectorator.

If you would like to learn more about the breaking changes related to the major version change for reselect, please visit the reselect CHANGELOG.

Usage

import createSelector from "selectorator";

// selector created with single method call
const getBarBaz = createSelector(
  ["foo.bar", "baz"],
  (bar, baz) => `${bar} ${baz}`
);

const state = {
  foo: { bar: "bar" },
  baz: "baz"
};

console.log(getBarBaz(state)); // "bar baz"

Not a whole lot of magic here, just simplifying the creation of the "identity selectors" that reselect requires, instead replacing them with a standardized dot- or bracket-notation string for retrieval of a nested property in the state object.

That said, you can still use your own custom identity selectors, or compose selectors, if you so choose. Here is the example from the reselect README modified to use selectorator:

// subtotal built using simple method
const getSubtotal = createSelector(
  ["shop.items"],
  items => items.reduce((sum, { value }) => sum + value, 0)
);

// tax built with simple method combined with other selector
const getTax = createSelector(
  [getSubtotal, "shop.taxPercent"],
  (subtotal, taxPercent) => subtotal * (taxPercent / 100)
);

// total build entirely with other selectors
const getTotal = createSelector(
  [getSubtotal, getTax],
  (subtotal, tax) => ({ total: subtotal + tax })
);

const state = {
  shop: {
    taxPercent: 8,
    items: [{ name: "apple", value: 1.2 }, { name: "orange", value: 0.95 }]
  }
};

console.log("subtotal: ", getSubtotal(state)); // 2.15
console.log("tax: ", getTax(state)); // 0.172
console.log("total: ", getTotal(state)); // {total: 2.322}

Shorthand types

The following types of shorthand are available for parameter selector creation:

• Pulls from state:
  • string => 'foo[0].bar'
  • number => 0
  • Array => ['foo', 0, 'bar']
• Pulls from specific argument:
  • Object => {path: 'foo[0].bar', argIndex: 1}

Please note that the Object usage is the only approach that will allow for selection of parameters. All other shorthands will pull from the first parameter.

TypeScript

Selectorator now supports two optional type parameters, it accepts an Input type param (usually the redux state) and the expected output type.

When creating a selector that accepts multiple params, the state should be array of the input types example

i.e createSelector<[State, number[], boolean], string>

  import createSelector from "selectorator";

  interface State {
    foo: {
      bar: string;
    };
    baz: string;
  };
                        // State is input type, string is output type
  const getBarBaz = createSelector<State, string>(
    ["foo.bar", "baz"],
    (bar, baz) => `${bar} ${baz}`
  );

  // getBarBaz() has type signature: (state: State) => string;

  const getBarBaz2 = createSelector<any, string>(
    ["foo.bar", "baz"],
    (bar, baz) => `${bar} ${baz}`
  );

  // getBarBaz2() has type signature: (state: any) => string;

  const getBarBaz3 = createSelector(
    ["foo.bar", "baz"],
    (bar, baz) => `${bar} ${baz}`
  );

  // getBarBaz3() has type signature: (state: any) => any;

  const getBarBaz4 = createSelector(
    ["foo.bar", "baz", { path: 0, argIndex: 2 }],
    (bar, baz) => `${bar} ${baz}`
  );

  // getBarBaz4() has type signature: (...state: any[]) => any;

  const getBarBazQux5 = createSelector<[State, string[]], string>(
    ["foo.bar", "baz", { path: 0, argIndex: 2 }],
    (bar, baz) => `${bar} ${baz}`
  );

  // getBarBaz5() has type signature: (state_0: State, state_1: string[]) => string;

  const getStucturedBarBaz = createSelector({ barBaz: getBarBaz });

  // getStructuredBarBaz() has type signature: (state: any) => ({ barBaz: string });

Options

All the capabilities that exist with reselect are still available using selectorator, they are just passed as an object of options to createSelector.

deepEqual

defaults to false

A common usage of custom selectors is to perform a deep equality check instead of the standard strict equality check when comparing values. To apply this, simply set deepEqual to true.

import createSelector from "selectorator";

const selectoratorOptions = { deepEqual: true };

const getBaz = createSelector(
  ["foo.bar.baz"],
  baz => !!baz,
  selectoratorOptions
);

isEqual

defaults to isSameValueZero

If you want to use a custom equality comparator, pass the method as this option.

import createSelector from "selectorator";

const selectoratorOptions = {
  // silly example checking current or next values related to "foo"
  isEqual(currentFoo, nextFoo) {
    return currentFoo === "foo" || nextFoo !== "foo";
  }
};

const getFoo = createSelector(
  ["foo"],
  foo => !!foo,
  selectoratorOptions
);

Please note that if this parameter is provided and deepEqual is also set to true, deepEqual will take priority and the isEqual method will not be used.

memoizer

defaults to reselect defaultMemoize

If you want to use a custom memoizer, pass the method as this option. This will use createSelectorCreator from reselect internally, so consult their documentation on proper usage.

import createSelector from "selectorator";
import moize from "moize";

const selectoratorOptions = { memoizer: moize };

const getFoo = createSelector(
  ["foo"],
  foo => !!foo,
  selectoratorOptions
);

memoizerParams

defaults to []

reselect allows you to pass parameters to the memoizer function, and this array will translate directly into parameters 3-n. This is useful if your memoizer uses something other than direct comparison for its equality test.

import createSelector from "selectorator";

const selectoratorOptions = {
  memoizer: memoizerThatChecksEqualToEachOtherOrToSpecificValuePassed,
  memoizerParams: ["specificValue"]
};

const getFoo = createSelector(
  ["foo"],
  foo => !!foo,
  selectoratorOptions
);

Development

Standard stuff, clone the repo and npm install dependencies. The npm scripts available:

• build => run webpack to build development dist file with NODE_ENV=development
• build:minifed => run webpack to build production dist file with NODE_ENV=production
• dev => run webpack dev server to run example app (playground!)
• docs => builds the docs via jsdoc
• lint => run ESLint against all files in the src folder
• prepublish => runs prepublish:compile
• prepublish:compile => run lint, test:coverage, transpile, build, build:minified, and docs
• test => run AVA test functions with NODE_ENV=test
• test:coverage => run test but with nyc for coverage checker
• test:watch => run test, but with persistent watcher
• transpile => run babel against all files in src to create files in lib