Creating Unique Symbols
Generate guaranteed-unique values.
Creating Unique Symbols is a free JavaScript Academy lesson on CoddyKit — lesson 1 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the JavaScript Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
What Is a Symbol
A Symbol is a primitive type introduced in modern JavaScript. Every symbol is unique, even if two symbols share the same description.
const s = Symbol()
console.log(typeof s)Creating a Symbol
You create a symbol by calling the Symbol function. It is not a constructor, so you never use new with it.
const id = Symbol()
console.log(typeof id)Optional Description
You can pass a description string to help with debugging. The description is purely informational and does not affect uniqueness.
const id = Symbol("user id")
console.log(id.description)Every Symbol Is Unique
Two symbols are never equal, even with identical descriptions. This guaranteed uniqueness is their defining feature.
const a = Symbol("x")
const b = Symbol("x")
console.log(a === b)No New Keyword
Calling Symbol with new throws an error, because symbols are primitives, not objects. Always call it as a plain function.
const s = Symbol("ok")
console.log(typeof s === "symbol")Symbols Are Primitives
The typeof a symbol is the string symbol. Like other primitives, symbols are immutable and have no properties to change.
const s = Symbol("p")
console.log(typeof s)Reading the Description
The description property returns the text you supplied, or undefined if none was given. It is read-only.
const named = Symbol("hello")
const anon = Symbol()
console.log(named.description)
console.log(anon.description)Symbols Cannot Coerce to String
Symbols do not implicitly convert to strings, which prevents accidental misuse. Use String or toString to get text deliberately.
const s = Symbol("tag")
console.log(String(s))
console.log(s.toString())Using Symbols as Constants
Symbols make excellent unique constant values, for example to represent distinct states that can never collide.
const RED = Symbol("red")
const GREEN = Symbol("green")
console.log(RED === GREEN)Storing Symbols
You can store symbols in variables, arrays, and as values inside objects. Their uniqueness travels with them.
const states = [Symbol("on"), Symbol("off")]
console.log(states.length)
console.log(states[0] === states[1])Why Uniqueness Matters
Because no two symbols collide, they are ideal for keys that must never clash with other code, which we explore in the next lesson.
const key1 = Symbol("meta")
const key2 = Symbol("meta")
const obj = {}
obj[key1] = "a"
obj[key2] = "b"
console.log(obj[key1], obj[key2])Quick Check
Test your symbol creation knowledge.
Recap
Recap: Symbols are unique primitive values.
- Created by calling Symbol, never with new
- Optional description aids debugging only
- Every symbol is unique
- typeof a symbol is symbol
const a = Symbol("x")
const b = Symbol("x")
console.log(a === b)Frequently asked questions
Is the “Creating Unique Symbols” lesson free?
Yes — the full text of “Creating Unique Symbols” is free to read here on the web, and the JavaScript Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the JavaScript Academy course, upgrade to CoddyKit PRO.
What will I learn in “Creating Unique Symbols”?
Generate guaranteed-unique values. You practise JavaScript Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start JavaScript Academy?
No prior experience is required. JavaScript Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 1 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Creating Unique Symbols” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this JavaScript Academy lesson?
Yes. Every JavaScript Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Creating Unique Symbols
- Symbols as Object Keys
- The Global Symbol Registry
- Well-Known Symbols