var primitives = [ ["string", String.prototype], [42, Number.prototype], [Symbol("symbol"), Symbol.prototype], [true, Boolean.prototype], [false, Boolean.prototype] ]; for (var [primitive, expected] of primitives) { var ret = Object.getPrototypeOf(primitive); if (ret !== expected) throw new Error("bad value for " + String(primitive) + ": " + String(ret)); } [ [ null, "TypeError: null is not an object (evaluating 'Object.getPrototypeOf(value)')" ], [ undefined, "TypeError: undefined is not an object (evaluating 'Object.getPrototypeOf(value)')" ] ].forEach(function ([value, message]) { var error = null; try { Object.getPrototypeOf(value); } catch (e) { error = e; } if (!error) throw new Error("error not thrown"); if (String(error) !== message) throw new Error("bad error: " + String(error)); });