First Arg Reselect

firstArgSelector.js

/* eslint-disable import/prefer-default-export */
// @flow
import { createSelectorCreator } from 'reselect';

const defaultEqualityCheck = (a, b) => (a === b);

/**
 * A selector that will only change the output if the first argument has changed.
 */
export const firstArgSelector = createSelectorCreator(
  (func, equalityCheck = defaultEqualityCheck) => {
    let lastArg = null;
    let lastResult = null;
    return (...args) => {
      if (
        lastArg !== null &&
        equalityCheck(lastArg, args[0])
      ) {
        return lastResult;
      }
      lastArg = args[0];
      lastResult = func(...args);
      return lastResult;
    };
  });