Dict sum common items

function makeOccurrenceCounter(arr) {
    const occDict = {};

    for(let item of arr) {
        if(occDict[item]) {
            occDict[item]++;
        } else {
            occDict[item] = 1;
        }
    }

    return occDict;
}

function common(arr1, arr2, arr3) {
    const [occ1, occ2, occ3] = [
        makeOccurrenceCounter(arr1),
        makeOccurrenceCounter(arr2),
        makeOccurrenceCounter(arr3),
    ];

    const minOcc = {};

    const merged = [...arr1, ...arr2, ...arr3];

    for(let item of merged) {
        minOcc[item] = Math.min(
            occ1[item] || 0,
            occ2[item] || 0,
            occ3[item] || 0,
        )
    }

    return minOcc;
}