symbol.md

Symbols

What

• Like strings or UIDs, but guaranteed to be unique
• (almost) private
• low usefulness-to-comprehensibility ratio

Symbols have nothing to do with Ruby symbols (:ruby_symbol)

How

Create symbols (don't use new!)

Symbol() === Symbol() // false

You can associate a symbol with a string for debugging purposes

Symbol('foo') === Symbol('foo') // false
console.log(Symbol('foo')) // "Symbol('foo')"

Why

One use case: Use like private properties for encapsulation

const privateMethodKey = Symbol('privateMethod')

class Foo {
	constructor(){
		
		this[privateMethodKey] = () => 42
	}
	sayHello(){
		console.log('hi')
	}
}

Quiz

What will this code print?

const foo = new Foo()
const newSymbol = Symbol('privateMethodKey')

console.log(Object.keys(foo))
console.log(foo[newSymbol])
console.log(foo[privateMethodKey])

Other Uses:

• used internally in JS (example: Symbol.iterator)
• use like enums
• monkey patching