function shouldBe(actual, expected) { if (actual !== expected) throw new Error('bad value: ' + actual); } function shouldThrow(func, errorMessage) { var errorThrown = false; var error = null; try { func(); } catch (e) { errorThrown = true; error = e; } if (!errorThrown) throw new Error('not thrown'); if (String(error) !== errorMessage) throw new Error(`bad error: ${String(error)}`); } var func = Map.prototype.set; function target(map) { return func.call(map, 42, 42); } noInline(target); for (var i = 0; i < 1e6; ++i) { var map = new Map(); shouldBe(target(map), map); shouldBe(map.get(42), 42); } shouldThrow(() => { target(new Set()); }, `TypeError: Map operation called on non-Map object`);