Multiple fields comparator

comparators.js

export function compareByField(field, reverse, predicate) {
    const key = predicate ? x => predicate(x[field]) : x => x[field]
    reverse = !reverse ? 1 : -1

    return (a, b) => {
        const key_a = key(a)
        const key_b = key(b)

        return reverse * ((key_a > key_b) - (key_b > key_a))
    }
}

/*
    Params description:

    sortingRules = [
        {columnName: 'field1', 'direction': 'asc'},
        {columnName: 'field2', 'direction': 'desc'},
    ]
    predicates = {
        'field1': (value) => value.toLowerCase()
    }
*/
export function compareByMultipleFields(sortingRules, predicates) {
    let comparators = sortingRules.map(sortingRule => {
        return compareByField(
            sortingRule.columnName,
            sortingRule.direction === 'desc',
            predicates[sortingRule.columnName] || null
        )
    })

    return (a, b) => {
        for (let comparator of comparators) {
            const comparisonResult = comparator(a, b)
            if (comparisonResult !== 0) return comparisonResult
        }
        return 0
    }
}