rax/src/vdom/shallowEqual.js

A universal React-compatible render engine.

import { isNull, isObject, EMPTY_OBJECT } from '../types';

const hasOwnProperty = EMPTY_OBJECT.hasOwnProperty;

/**
 * inlined Object.is polyfill to avoid requiring consumers ship their own
 * https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/is
 */
export 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;
  } else {
    // Step 6.a: NaN == NaN
    return x !== x && y !== y; // eslint-disable-line no-self-compare
  }
}

/**
 * Performs equality by iterating through keys on an object and returning false
 * when any key has values which are not strictly equal between the arguments.
 * Returns true when the values of all keys are strictly equal.
 */
export default function shallowEqual(objA, objB) {
  if (is(objA, objB)) {
    return true;
  }

  if (!isObject(objA) || isNull(objA) || !isObject(objB) || isNull(objB)) {
    return false;
  }

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

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

  // Test for A's keys different from B.
  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;
}