用于在两个对象或数组之间执行浅比较的函数。当两个值的所有成员都严格等于另一个值的对应成员时，这两个值具有浅相等。

用法

@wordpress/is-shallow-equal 的默认导出是一个接受两个对象或数组的函数：

import isShallowEqual from '@wordpress/is-shallow-equal';

isShallowEqual( { a: 1 }, { a: 1, b: 2 } );
// ⇒ false

isShallowEqual( { a: 1 }, { a: 1 } );
// ⇒ true

isShallowEqual( [ 1 ], [ 1, 2 ] );
// ⇒ false

isShallowEqual( [ 1 ], [ 1 ] );
// ⇒ true

如果你已经知道要处理的值类型，可以导入特定的实现：

import { isShallowEqualArrays } from '@wordpress/is-shallow-equal';
import { isShallowEqualObjects } from '@wordpress/is-shallow-equal';

浅比较与深比较的不同之处在于，它将每个值的成员与另一个值的成员进行严格相等比较，这意味着数组和对象将按其引用进行比较，而不是按其值进行比较（另见JavaScript 中的对象相等）。在必须按值比较嵌套对象的情况下，请考虑改用 fast-deep-equal。

import isShallowEqual from '@wordpress/is-shallow-equal';
import fastDeepEqual from 'fast-deep-equal/es6'; // 深比较

let object = { a: 1 };

isShallowEqual( [ { a: 1 } ], [ { a: 1 } ] );
// ⇒ false

fastDeepEqual( [ { a: 1 } ], [ { a: 1 } ] );
// ⇒ true

isShallowEqual( [ object ], [ object ] );
// ⇒ true

理由

浅相等工具已经比比皆是。由于这些操作通常位于关键热代码路径的核心，WordPress 贡献者有一些特定需求，而现有解决方案只能部分满足这些需求。

具体来说，它应该……

  1. ……将非原始但引用相等的成员值视为相等。
  2. ……提供单一函数作为接口，无论值类型如何。
  3. ……保持极简；仅提供浅相等的基础功能。
  4. ……预期并针对引用相同视为相等的情况进行优化。
  5. ……面向非 Facebook 项目使用。
  6. ……是性能最佳的实现。

基准测试

以下结果是在 Node v10.15.3（LTS）环境下，于 MacBook Pro（Late 2016）2.9 GHz Intel Core i7 上生成的。

@wordpress/is-shallow-equal (type specific) (object, equal) x 4,519,009 ops/sec ±1.09% (90 runs sampled) >@wordpress/is-shallow-equal (type specific) (object, same) x 795,527,700 ops/sec ±0.24% (93 runs sampled) >@wordpress/is-shallow-equal (type specific) (object, unequal) x 4,841,640 ops/sec ±0.94% (93 runs sampled) >@wordpress/is-shallow-equal (type specific) (array, equal) x 106,393,795 ops/sec ±0.16% (94 runs sampled) >@wordpress/is-shallow-equal (type specific) (array, same) x 800,741,511 ops/sec ±0.22% (95 runs sampled) >@wordpress/is-shallow-equal (type specific) (array, unequal) x 49,178,977 ops/sec ±1.99% (82 runs sampled)

@wordpress/is-shallow-equal (object, equal) x 4,449,367 ops/sec ±0.31% (91 runs sampled) >@wordpress/is-shallow-equal (object, same) x 796,677,179 ops/sec ±0.23% (94 runs sampled) >@wordpress/is-shallow-equal (object, unequal) x 4,989,529 ops/sec ±0.30% (91 runs sampled) >@wordpress/is-shallow-equal (array, equal) x 44,840,546 ops/sec ±1.18% (89 runs sampled) >@wordpress/is-shallow-equal (array, same) x 794,344,723 ops/sec ±0.24% (91 runs sampled) >@wordpress/is-shallow-equal (array, unequal) x 49,860,115 ops/sec ±1.73% (85 runs sampled)

shallowequal (object, equal) x 3,702,126 ops/sec ±0.87% (92 runs sampled) >shallowequal (object, same) x 796,649,597 ops/sec ±0.21% (92 runs sampled) >shallowequal (object, unequal) x 4,027,885 ops/sec ±0.31% (96 runs sampled) >shallowequal (array, equal) x 1,684,977 ops/sec ±0.37% (94 runs sampled) >shallowequal (array, same) x 794,287,091 ops/sec ±0.26% (91 runs sampled) >shallowequal (array, unequal) x 1,738,554 ops/sec ±0.29% (91 runs sampled)

shallow-equal (type specific) (object, equal) x 4,669,656 ops/sec ±0.34% (92 runs sampled) >shallow-equal (type specific) (object, same) x 799,610,214 ops/sec ±0.20% (95 runs sampled) >shallow-equal (type specific) (object, unequal) x 4,908,591 ops/sec ±0.49% (93 runs sampled) >shallow-equal (type specific) (array, equal) x 104,711,254 ops/sec ±0.65% (91 runs sampled) >shallow-equal (type specific) (array, same) x 798,454,281 ops/sec ±0.29% (94 runs sampled) >shallow-equal (type specific) (array, unequal) x 48,764,338 ops/sec ±1.48% (84 runs sampled)

is-equal-shallow (object, equal) x 5,068,750 ops/sec ±0.28% (92 runs sampled) >is-equal-shallow (object, same) x 17,231,997 ops/sec ±0.42% (92 runs sampled) >is-equal-shallow (object, unequal) x 5,524,878 ops/sec ±0.41% (92 runs sampled) >is-equal-shallow (array, equal) x 1,067,063 ops/sec ±0.40% (92 runs sampled) >is-equal-shallow (array, same) x 1,074,356 ops/sec ±0.20% (94 runs sampled) >is-equal-shallow (array, unequal) x 1,758,859 ops/sec ±0.44% (92 runs sampled)

shallow-equals (object, equal) x 8,380,550 ops/sec ±0.31% (90 runs sampled) >shallow-equals (object, same) x 27,583,073 ops/sec ±0.60% (91 runs sampled) >shallow-equals (object, unequal) x 8,954,268 ops/sec ±0.71% (92 runs sampled) >shallow-equals (array, equal) x 104,437,640 ops/sec ±0.22% (96 runs sampled) >shallow-equals (array, same) x 141,850,542 ops/sec ±0.25% (93 runs sampled) >shallow-equals (array, unequal) x 47,964,211 ops/sec ±1.51% (84 runs sampled)

fbjs/lib/shallowEqual (object, equal) x 3,366,709 ops/sec ±0.35% (93 runs sampled) >fbjs/lib/shallowEqual (object, same) x 794,825,194 ops/sec ±0.24% (94 runs sampled) >fbjs/lib/shallowEqual (object, unequal) x 3,612,268 ops/sec ±0.37% (94 runs sampled) >fbjs/lib/shallowEqual (array, equal) x 1,613,800 ops/sec ±0.23% (90 runs sampled) >fbjs/lib/shallowEqual (array, same) x 794,861,384 ops/sec ±0.24% (93 runs sampled) >fbjs/lib/shallowEqual (array, unequal) x 1,648,398 ops/sec ±0.77% (92 runs sampled)

你可以通过克隆仓库、安装依赖并运行 benchmark/index.js 脚本来自行运行基准测试：

git clone https://github.com/WordPress/gutenberg.git
npm install
npm run build
node ./packages/is-shallow-equal/benchmark

为这个包做出贡献

这是 Gutenberg 项目中的一个独立包。该项目组织为 monorepo。它由多个自包含的软件包组成，每个包都有特定用途。此 monorepo 中的包会发布到 npm，并被 WordPress 以及其他软件项目使用。

要了解更多关于为该包或整个 Gutenberg 项目做出贡献的信息，请阅读项目的主要 贡献者指南。