//// [privateInstanceMemberAccessibility.ts] class Base { private foo: string; } class Derived extends Base { x = super.foo; // error y() { return super.foo; // error } z: typeof super.foo; // error a: this.foo; // error } //// [privateInstanceMemberAccessibility.js] var __extends = (this && this.__extends) || function (d, b) { for (var p in b) if (b.hasOwnProperty(p)) d[p] = b[p]; function __() { this.constructor = d; } d.prototype = b === null ? Object.create(b) : (__.prototype = b.prototype, new __()); }; var Base = (function () { function Base() { } return Base; })(); var Derived = (function (_super) { __extends(Derived, _super); function Derived() { _super.apply(this, arguments); this.x = _super.prototype.foo; // error this.z = _super.prototype.foo; // error this.a = this.foo; // error } Derived.prototype.y = function () { return _super.prototype.foo; // error }; return Derived; })(Base);