What is a symbol type?

Symbol Type

Only two primitive types can serve as keys for properties in objects.

• string type
• symbol type

Otherwise, if one uses another type, such as number, it’s autoconverted to string. So that obj[1] is the same as obj["1"], and obj[true] is the same as obj["true"].

Until now we’ve been using only strings.

Now let’s explore symbols, see what they can do for us.

Symbol

A “symbol” represents a unique identifier.

A value of this type can be created using Symbol():

let id = Symbol();

Upon creation, we can give symbols a description (also called a symbol name), mostly useful for debugging purposes:

// id is a symbol with the description "id"
let id = Symbol("id");

Symbols are guaranteed to be unique. Even if we create many symbols with exactly the same description, they are different values. The description is just a label that doesn’t affect anything.

For instance, here are two symbols with the same description – they are not equal:

let id1 = Symbol("id");
let id2 = Symbol("id");

alert(id1 == id2); // false

So, to summarize, a symbol is a “primitive unique value” with an optional description. Let’s see where we can use them.