How To Hack JavaScript With Well-Known Symbols (5 Ways)

They call them well-known symbols — even though most developers have never used them or even heard of them.

A really cool feature you can use to make magic like this happen:

You’ll see how we built these classes with well-known symbols to do this.

They’re all about completely customizing the normal behavior of built-in operations like for..of. It's like operator overloading in C++ and C#.

Also all static methods of the Symbol class.

1. Symbol.hasInstance

So first up we have Symbol.hasInstance: for easily changing how the instanceof operator behaves.

Normally instanceof is all about checking if a variable is an instance of class.