function Constructor(x) {} Object.defineProperty(Constructor, Symbol.hasInstance, {value: function() { return false; }}); x = new Constructor(); function instanceOf(a, b) { return a instanceof b; } noInline(instanceOf); function body() { var result = 0; for (var i = 0; i < 100000; i++) { if (instanceOf(x, Constructor)) result++; } return result; } noInline(body); if (body()) throw "result incorrect";