tests/cases/conformance/salsa/a.js(28,24): error TS2339: Property 'addon' does not exist on type '{ set: () => void; get(): void; }'. ==== tests/cases/conformance/salsa/a.js (1 errors) ==== // non top-level: // all references to _map, set, get, addon should be ok (function container() { /** @constructor */ var Multimap = function() { this._map = {}; this._map this.set this.get this.addon }; Multimap.prototype = { set: function() { this._map this.set this.get this.addon }, get() { this._map this.set this.get this.addon } } Multimap.prototype.addon = function () { ~~~~~ !!! error TS2339: Property 'addon' does not exist on type '{ set: () => void; get(): void; }'. this._map this.set this.get this.addon } var mm = new Multimap(); mm._map mm.set mm.get mm.addon });