function exec(vf) {
    if (this.dataRow) {
        var calculator = (typeof vf)[0] === 'f' && vf || this.calculator;
        if (calculator) {
            vf = calculator(this.dataRow, this.name, this.subrow);
        }
    }
    return vf;
}
@summary Execute value if "calculator" (function) or if column has calculator.
@desc This function is referenced here so:
1. It will be available to the cell renderers
2. Its context will naturally be the `config` object
@default {@link module:defaults.exec|exec}
@method
@param vf - Value or function.
@memberOf module:defaults