js实现归并排序

const Compare={
    LESS_THAN:-1,
    BIGGER_THAN:1,
    EQUAL:0,
}
function defaultCompare(a,b){
    return a === b?Compare.EQUAL: a > b ?Compare.BIGGER_THAN:Compare.LESS_THAN;
}
function mergeSort(array, compareFn = defaultCompare) {
    if(array.length > 1){
        const { length } = array;
        const middle = Math.floor(length / 2);
        const left = mergeSort(array.slice(0,middle),compareFn);
        const right = mergeSort(array.slice(middle,length),compareFn);
        array = merge(left,right,compareFn);
    }
    return array;
}
function merge(left,right,compareFn){
    let i = 0;
    let j = 0;
    const result = [];
    while(i < left.length && j < right.length){
        result.push(compareFn(left[i],right[j]) === Compare.LESS_THAN ? left[i++]:right[j++]);
    }
    return result.concat(i < left.length ? left.slice(i) : right.slice(j));
}