v8/test/mjsunit/es6/regress/regress-2156.js

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// Flags: --allow-natives-syntax

var key1 = {};
var key2 = {};
var map = new WeakMap;

// Adding hidden properties preserves map sharing. Putting the key into
// a WeakMap will cause the first hidden property to be added.
assertTrue(%HaveSameMap(key1, key2));
map.set(key1, 1);
map.set(key2, 2);
assertTrue(%HaveSameMap(key1, key2));