test/mjsunit/regress/negative_lookup.js

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function s(v) {
  v.x = 1;
}

function c(p) {
  return {__proto__: p};
}

var p = {};

// Make p the last prototype in the chain.
p.__proto__ = null;

var o1 = c(p);
var o2 = c(p);
var o3 = c(p);
var o4 = c(p);

// Make y go to slow mode.
// Do this after using p as prototype, since using an object as prototype kicks
// it back into fast mode.
p.y = 1;
delete p.y;

// Initialize the store IC.
s(o1);
s(o2);

// Do something with x in slow-mode p.
Object.defineProperty(p, "x", { writable: false, value: 5 });

// Verify that directly setting x fails.
o3.x = 10;
assertEquals(5, o3.x);

// Verify that setting x through the IC fails.
s(o4);
assertEquals(5, o4.x);