boom.js

function crash(obj) {
 return obj.foo;
}

function base(number_of_properties) {
 var result = new Array();
 for (var i = 0; i < number_of_properties; i++) {
   result["property" + i] = "value" + i;
  } 
  result.foo = number_of_properties;
  return result;
}

var a = base(12);
var b = base(13);
var c = base(14);
var d = base(15);

crash(a);
crash(b);
crash(c);
crash(d); // Polymorphic, degree 4.

for (i = 0; i < 260; i++)
  crash(a);

//Prepare ElementsKind transition map chain.
var x = base(13);
x[0] = "object";
x = base(14);
x[0] = "object";
x = base(15);
x[0] = "object";

console.log("almost");

setTimeout(function() {
  crash(a);
  console.log("done");
}, 500);