How to use JavaScript to add elements at the end of an array and perform deduplication and reverse order operations?

Add elements, deduplication and inverse order at the end of JavaScript array

This article introduces a JavaScript function that implements adding new elements to the end of the array, ensuring element uniqueness, and returning the inverse result of the last three elements of the array. The function receives the array list and the new element object newElement as parameters.

The function first determines whether list is an array, and if not, it is initialized as an empty array. It then uses a helper function isSameObject to compare whether all fields of the two objects are exactly the same. If the same element as newElement is found, it is removed from list . After that, newElement is added to the end of list . Finally, the function returns an inverse array of the last three elements in list .

The following is the code implementation:

 function updateList(list, newElement) {
    // Initialize to an empty array, if list is not an array if (!Array.isArray(list)) {
        list = [];
    }

    // Compare whether two objects are exactly the same const isSameObject = (obj1, obj2) => {
        return Object.keys(obj1).length === Object.keys(obj2).length &&
               Object.keys(obj1).every(key => obj1[key] === obj2[key]);
    };

    // Find and delete the same element as newElement const index = list.findIndex(item => isSameObject(item, newElement));
    if (index !== -1) {
        list.splice(index, 1);
    }

    // Add new element to the end of the array list.push(newElement);

    // Return the inverse array of the last three elements return list.slice(-3).reverse();
}


// Test case let list1 = [
    { id: 2 },
    { id: 3 },
    { id: 4 }
];
let newElement1 = { id: 2 };
console.log(updateList(list1, newElement1)); // Output: [{id: 2}, {id: 3}, {id: 4}]


let list2 = [
    { id: 1 },
    { id: 2 },
    { id: 3 },
    { id: 4 }
];
let newElement2 = { id: 3 };
console.log(updateList(list2, newElement2)); // Output: [{id: 3}, {id: 1}, {id: 2}]


let list3 = [
    { id: 1 },
    { id: 2 },
    { id: 3 },
    { id: 4 }
];
let newElement3 = { id: 5 };
console.log(updateList(list3, newElement3)); // Output: [{id: 5}, {id: 2}, {id: 3}]

let list4 = [];
let newElement4 = {id:1};
console.log(updateList(list4, newElement4)); // Output: [{id: 1}]

This function effectively handles array addition, deduplication, and reverse order operations, and provides clear code structure and test cases. isSameObject function ensures accurate depth comparison of objects and avoids errors that may be caused by shallow comparisons.

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