Simple DSL for composing sorting logic

compileSort.js

// Convert a sorting expressions (e.g. "Outflow DESC; Date ASC; Category ASC")
// into a function that can be passed to Array.prototype.sort.
function compileSort(expr) {
    if (expr === '') {
        return function(x, y) { return 0; };
     }
    return expr.split(/\s*;\s*/).reverse().reduce((acc, x) => {
        const [k, dir] = x.split(/\s+/);
        if (dir === 'ASC') {
            return function(x, y) {
                if (x[k] > y[k]) { return 1; }
                if (x[k] < y[k]) { return -1; }
                else { return acc(x, y); }
            };
        }
        if (dir === 'DESC') {
            return function(x, y) {
                if (x[k] > y[k]) { return -1; }
                if (x[k] < y[k]) { return 1; }
                else { return acc(x, y); }
            };
        }
        else {
            throw new Error(`Sort direction not supported, ${dir}, must be either "ASC" or "DESC"`);
        }
    }, function(x, y) { return 0; })
}