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How can I merge two arrays of objects based on a common key without duplicates in JavaScript?

Asked on Nov 13, 2025

Answer

To merge two arrays of objects based on a common key without duplicates, you can use the "reduce" and "map" methods to create a new array that combines both arrays while ensuring unique entries based on the specified key.
<!-- BEGIN COPY / PASTE -->
        const array1 = [
            { id: 1, name: "John" },
            { id: 2, name: "Jane" }
        ];

        const array2 = [
            { id: 2, name: "Jane" },
            { id: 3, name: "Doe" }
        ];

        const mergedArray = [...array1, ...array2].reduce((acc, current) => {
            const x = acc.find(item => item.id === current.id);
            if (!x) {
                acc.push(current);
            }
            return acc;
        }, []);

        console.log(mergedArray);
        <!-- END COPY / PASTE -->
Additional Comment:
  • This code merges "array1" and "array2" based on the "id" key.
  • The "reduce" function iterates over the combined array and checks if an object with the same "id" already exists in the accumulator "acc".
  • If an object with the same "id" is not found, the current object is added to the accumulator.
  • The result is a merged array without duplicates based on the "id" key.
✅ Answered with JavaScript best practices.
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