prettier/website/playground/helpers.js

export function stateToggler(key) {
  return state => ({ [key]: !state[key] });
}

const hasOwnProperty = Object.prototype.hasOwnProperty;

function is(x, y) {
  // SameValue algorithm
  if (x === y) {
    // Steps 1-5, 7-10
    // Steps 6.b-6.e: +0 != -0
    return x !== 0 || 1 / x === 1 / y;
  }
  // Step 6.a: NaN == NaN
  return x !== x && y !== y;
}

export function shallowEqual(objA, objB) {
  if (is(objA, objB)) {
    return true;
  }

  if (
    typeof objA !== "object" ||
    objA === null ||
    typeof objB !== "object" ||
    objB === null
  ) {
    return false;
  }

  const keysA = Object.keys(objA);
  const keysB = Object.keys(objB);

  if (keysA.length !== keysB.length) {
    return false;
  }

  for (let i = 0; i < keysA.length; i++) {
    if (
      !hasOwnProperty.call(objB, keysA[i]) ||
      !is(objA[keysA[i]], objB[keysA[i]])
    ) {
      return false;
    }
  }

  return true;
}