Another RPG Engine stat class code

window.Stat = class Stat {
	constructor (base) {
        this._base = base;
        this._mods = {};
        this._current = undefined;
	}

    clearCache () {
		this._current = undefined;
    }

    addMod (id, mod) {
        id = String(id);
        if(Number.isFinite(mod)) {
            mod = { add: mod };
        }
        if(typeof mod === "object") {
            this._mods[id] = mod;
            this.clearCache();
        }
    }

    removeMod (id) {
        delete this._mods[String(id)];
        this.clearCache();
    }

    clearMods () {
        this._mods = {};
        this.clearCache();
    }

	get base () {
        return this._base;
    }

	set base (newBase) {
        newBase = Number(newBase);
        /* alternative: newBase = setup.roll(newBase) for "3d6" as inputs */
        if(!Number.isFinite(newBase)) {
            newBase = 0;
        }
        if (this._base !== newBase) {
            this._base = newBase;
            this.clearCache();
        }
    }

	get current () {
        if (this._current === undefined) {
            /* gather multipliers */
            var mult = Object.values(this._mods)
				.map(function(m) { return Number.isFinite(m.mult) ? m.mult : 0; })
				.reduce(function(sum, add) { return sum + add; }, 0);
            var add = Object.values(this._mods)
				.map(function(m) { return Number.isFinite(m.add) ? m.add : 0; })
				.reduce(function(sum, add) { return sum + add; }, 0);
            this._current = this.base * (mult + 1) + add;
        }
            return this._current;
    }

	toString () {
        var mult = Object.values(this._mods)
			.map(function(m) { return Number.isFinite(m.mult) ? m.mult : 0; })
            .reduce(function(sum, add) { return sum + add; }, 0);
        var add = Object.values(this._mods)
            .map(function(m) { return Number.isFinite(m.add) ? m.add : 0; })
            .reduce(function(sum, add) { return sum + add; }, 0);
        return this.current.toFixed(2)
            + " [" + this.base.toFixed(2)
            + " x " + (mult + 1).toFixed(2)
            + (add >= 0 ? " + " + add.toFixed(2) : " - " + (-add).toFixed(2))
            + "]";
    }

	/* SugarCube support */
    clone () {
        return Stat.create(this);
    }

	toJSON () {
        return JSON.reviveWrapper('setup.Stat.create($ReviveData$)', Object.assign({}, clone(this)));
    }
};

Stat.prototype.create = function(vals) {
    vals = vals || {};
    var result = new Stat();
    result._base = vals._base;
    result._mods = clone(vals._mods);
    result._current = vals._current;
    return result;
};