lodash lets me check for membership of basic data types with includes
:
_.includes([1, 2, 3], 2)
> true
But the following doesn't work:
_.includes([{"a": 1}, {"b": 2}], {"b": 2})
> false
This confuses me because the following methods that search through a collection seem to do just fine:
_.where([{"a": 1}, {"b": 2}], {"b": 2})
> {"b": 2}
_.find([{"a": 1}, {"b": 2}], {"b": 2})
> {"b": 2}
What am I doing wrong? How do I check for the membership of an object in a collection with includes
?
edit: question was originally for for lodash version 2.4.1, updated for lodash 4.0.0
This question is related to
javascript
functional-programming
lodash
You could use find
to solve your problem
const data = [{"a": 1}, {"b": 2}]
const item = {"b": 2}
find(data, item)
// > true
Supplementing the answer by p.s.w.g
, here are three other ways of achieving this using lodash
4.17.5
, without using _.includes()
:
Say you want to add object entry
to an array of objects numbers
, only if entry
does not exist already.
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}]
If you want to return a Boolean
, in the first case, you can check the index that is being returned:
_.findIndex(numbers, (o) => { return _.isMatch(o, entry) }) > -1;
// output: true
Source: Stackoverflow.com