No one has mentioned it yet, so Symbols would also be a way to go:
Symbol.for(new Date("Peter")) === Symbol.for("Invalid Date") // trueSymbol.for(new Date()) === Symbol.for("Invalid Date") // falseconsole.log('Symbol.for(new Date("Peter")) === Symbol.for("Invalid Date")', Symbol.for(new Date("Peter")) === Symbol.for("Invalid Date")) // trueconsole.log('Symbol.for(new Date()) === Symbol.for("Invalid Date")', Symbol.for(new Date()) === Symbol.for("Invalid Date")) // falseBe aware of:https://caniuse.com/#search=Symbol