memoize-one/lib/index.js.flow

A memoization library which only remembers the latest invocation

// @flow
type EqualityFn = (a: any, b: any) => boolean;

const simpleIsEqual = (a: any, b: any): boolean => a === b;

export default function (resultFn: Function, isEqual?: EqualityFn = simpleIsEqual) {
  let lastThis: any;
  let lastArgs: Array<any> = [];
  let lastResult: any;
  let calledOnce: boolean = false;

  const isNewArgEqualToLast = (newArg, index) => isEqual(newArg, lastArgs[index]);

    // breaking cache when context (this) or arguments change
  return function (...newArgs: Array<any>) {
    if (calledOnce &&
            lastThis === this &&
            newArgs.length === lastArgs.length &&
            newArgs.every(isNewArgEqualToLast)) {
      return lastResult;
    }

    calledOnce = true;
    lastThis = this;
    lastArgs = newArgs;
    lastResult = resultFn.apply(this, newArgs);
    return lastResult;
  };
}