lodash让我使用以下命令检查基本数据类型的成员资格includes
:
_.includes([1, 2, 3], 2)
> true
但是以下操作无效:
_.includes([{"a": 1}, {"b": 2}], {"b": 2})
> false
这使我感到困惑,因为以下搜索集合的方法似乎还不错:
_.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?如何使用来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,针对lodash版本4.0.0更新的
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,因为只有以下一个实例{"b": 2}
:
var a = {"a": 1}, b = {"b": 2};
_.includes([a, b], b);
> true
另一方面,where
(在v4中已弃用)和find
方法通过属性比较对象,因此它们不需要引用相等。作为的替代方法includes
,您可能想要尝试some
(也别名为any
):
_.some([{"a": 1}, {"b": 2}], {"b": 2})
> true
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。numbers
entry
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
您可以find
用来解决问题
const data = [{"a": 1}, {"b": 2}]
const item = {"b": 2}
find(data, item)
// > true
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文章标签:functional-programming , javascript , lodash
版权声明:本文为原创文章,版权归 javascript 所有,欢迎分享本文,转载请保留出处!
文章标签:functional-programming , javascript , lodash
版权声明:本文为原创文章,版权归 javascript 所有,欢迎分享本文,转载请保留出处!
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