function e(e, a) {
        for (var r = 1; void 0 !== r; ) {
            var s = -1 & r
              , c = r >> -(1 / 0)
              , b = -1 & c;
            switch (s) {
            case 0:
                !function() {
                    b
                }();
                break;
            case 1:
                var k = e.indexOf(a)
                  , t = -1
                  , o = k === t;
                r = o ? 2 : 3;
                break;
            case 2:
                return e;
            case 3:
                var i = e.substr(0, k);
                return i
            }
        }
    }

其中有个 void 0 !== r 是什么意思