Check for duplicates before adding to javascript array

Question

I have a React function, where I want to add an object to a javascript array. So far I have this

 selectAnimalHandler = (animal) =>{
    console.log(animal.id)
    if(this.state.animals.find(ani => ani !== animal )){
    this.setState(prevState =>(
        {selectedAnimals: [...prevState.selectedAnimals, animal]}))
    }
}

the logic is to check rather an element already exist in an array, and if it does not exist add it to the array. I try to make a condition, rather the element exists in the array or not. if it does not exist, nothing happens

Possible duplicate of [How to determine if object is in array](https://stackoverflow.com/questions/4587061/how-to-determine-if-object-is-in-array) — Terry, Jan 08 '19 at 21:44

score 2 · Accepted Answer · answered Jan 08 '19 at 21:44

2

This statement this.state.animals.find(ani => ani !== animal ) returns a value even if animal is in the array.

You should use something like this !this.state.animals.find(ani => ani === animal )

Also, keep in mind that === or even == used on objects is only true if you compare two references to the same thing.

answered Jan 08 '19 at 21:44

Titus

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inside a condition? – Kristoffer Tølbøll Jan 08 '19 at 21:48
@baileyhaldwin I'm not sure what you mean. The equal thing is true inside of conditions, – Titus Jan 08 '19 at 21:50
The condition returns false everytime – Kristoffer Tølbøll Jan 08 '19 at 21:52
@baileyhaldwin That is probably because `this.state.animals` contains objects and `animal` is not an object from inside that array. – Titus Jan 08 '19 at 21:53
@baileyhaldwin You should use something like `!this.state.animals.find(ani => ani.id === animal.id )` – Titus Jan 08 '19 at 21:54
to add to my state? – Kristoffer Tølbøll Jan 08 '19 at 22:01
@baileyhaldwin I don't know, I'm not sure what `this.state.animals` or `animals` look like. – Titus Jan 08 '19 at 22:02

Check for duplicates before adding to javascript array

1 Answers1