如何在lodash中使用includes方法来检查对象是否在集合中？

Question

lodash让我检查基本数据类型的成员资格includes:

_.includes([1, 2, 3], 2)
> true

但以下不起作用:

_.includes([{"a": 1}, {"b": 2}], {"b": 2})
> false

这让我感到困惑,因为以下搜索集合的方法似乎做得很好:

_.where([{"a": 1}, {"b": 2}], {"b": 2})
> {"b": 2}
_.find([{"a": 1}, {"b": 2}], {"b": 2})
> {"b": 2}

我究竟做错了什么？如何检查集合中对象的成员资格includes？

编辑:问题最初是针对lodash版本2.4.1,更新为lodash 4.0.0

Answer 1

的includes(以前称为contains和include)方法比较由参考对象(或者更准确地说,用===).因为{"b": 2}示例中的两个对象文字表示不同的实例,所以它们不相等.注意:

({"b": 2} === {"b": 2})
> false

但是,这将起作用,因为只有一个实例{"b": 2}:

var a = {"a": 1}, b = {"b": 2};
_.includes([a, b], b);
> true

另一方面,where(在v4中弃用)和find方法按对象的属性进行比较,因此它们不需要引用相等.作为替代方案includes,您可能想尝试some(也有别名any):

_.some([{"a": 1}, {"b": 2}], {"b": 2})
> true

Answer 2

通过补充答案p.s.w.g，这里是实现这一使用其他三种方式lodash 4.17.5，而无需使用 _.includes()：

假设仅在 尚不存在entry的对象中添加对象。numbersentry

let numbers = [
    { to: 1, from: 2 },
    { to: 3, from: 4 },
    { to: 5, from: 6 },
    { to: 7, from: 8 },
    { to: 1, from: 2 } // intentionally added duplicate
];

let entry = { to: 1, from: 2 };

/* 
 * 1. This will return the *index of the first* element that matches:
 */
_.findIndex(numbers, (o) => { return _.isMatch(o, entry) });
// output: 0


/* 
 * 2. This will return the entry that matches. Even if the entry exists
 *    multiple time, it is only returned once.
 */
_.find(numbers, (o) => { return _.isMatch(o, entry) });
// output: {to: 1, from: 2}


/* 
 * 3. This will return an array of objects containing all the matches.
 *    If an entry exists multiple times, if is returned multiple times.
 */
_.filter(numbers, _.matches(entry));
// output: [{to: 1, from: 2}, {to: 1, from: 2}]

如果要返回Boolean，在第一种情况下，可以检查正在返回的索引：

_.findIndex(numbers, (o) => { return _.isMatch(o, entry) }) > -1;
// output: true