String argument for Array reduce function

Array.reduce.js

var A_reduce = [].reduce;
Array.prototype.reduce = function reduce (callback, initialValue) {
  var operator = callback;
  return typeof operator == 'string' && /^[ +*/%-><!&|^?,.]/.test(operator)
    ? eval(this.join(operator))
    : A_reduce.apply(this, arguments)
};

[1,2,3,4].reduce('+') // 10
[1,2,3,4].reduce('*') // 24

[2, 0, 1].reduce('&&') // 0
[2, 0, 1].reduce('||') // 2