Problem with the test for union set?

JavaScript
1

Tell us what’s happening:
Can somebody please explain why the union method does not pass the tests? All the tests i’ve done returns the right result.

Your code so far


class Set {
constructor() {
    this._collection = []
}

print() {
    return console.log(this._collection)
}

add(item) {
    if (this.has(item)) {
        return false
    }
    this._collection = [...this._collection, item]
    return true
}

remove(item) {
    if(this.has(item)) {
        this._collection = this._collection.filter(value => value !== item)
        return true
    }
    return false
}

size() {
    return this._collection.length
}

has(item) {
    return this._collection.indexOf(item) !== -1
}

union(set) {
    const setOnlyUniqueItems = set._collection.filter(item => !this.has(item))
    this._collection = [...this._collection, ...setOnlyUniqueItems]
    return this._collection
}
}

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User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/78.0.3904.97 Safari/537.36.

Challenge: Perform a Union on Two Sets

Link to the challenge:
https://www.freecodecamp.org/learn/coding-interview-prep/data-structures/perform-a-union-on-two-sets

2

union should return a new Set you are returning an Array from that method.