instanceof-by-symbol

Use a Symbol from the registry to identify instances across realms or module versions.

Usage

const { defineInstanceSymbol } = require('instanceof-by-symbol');

class MyClass {
}

defineInstanceSymbol(MyClass, "my-module/[email protected]");

Now MyClass instances tested using instanceof will be identified by the my-module/[email protected] symbol. Different copies or versions of the module loaded in different realms or installed by npm will be considered instanceof each other.

The onus is on the developer to:

• use a symbol identifier that will not (or is unlikely to) clash with others; including the module and version is recommended
• change the symbol when the class is no longer compatible so should no longer be considered equivalent

defineInstanceSymbol also returns MyClass in case you want to use a more fluid style. It also works with the arguments reversed.

const { defineInstanceSymbol } = require('instanceof-by-symbol');

const MyClass = defineInstanceSymbol("my-module/[email protected]", class {
});