JavaScript Symbol data type is a primitive data type, introduced in ECMAScript 2015. A symbol is a unique and immutable value that can be used as the key of an object property.
Use the Symbol() function to create a Symbol
const mySymbol = Symbol();Each time you call Symbol(), a new and unique symbol is created. You can also pass a string to the Symbol() function to create a named symbol:
const myNamedSymbol = Symbol('mySymbolName');Symbols can be used as keys in object properties, like this:
const myObj = {};
const mySymbol = Symbol('mySymbolName');
myObj[mySymbol] = 'Hello, world!';
console.log(myObj[mySymbol]); // 'Hello, world!'Symbol data type in JavaScript example
A simple example code adds a Symbol as an Object Key.
<!DOCTYPE html>
<html>
<body>
<script>
let id = Symbol("id");
let person = {
name: "John",
age: 25,
// adding symbol as a key
[id]: 101 // not "id": 123
};
console.log(person);
</script>
</body>
</html>Output:
There are a number of built-in methods that can be used with Symbol objects.
| Method | Description |
|---|---|
for() | Searches for existing symbols |
keyFor() | Returns a shared symbol key from the global symbol registry. |
toSource() | Returns a string containing the source of the Symbol object |
toString() | Returns a string containing the description of the Symbol |
valueOf() | Returns the primitive value of the Symbol object. |
Symbols also have a few built-in properties that are accessible using the Symbol global object.
Symbol.iterator: A well-known symbol that represents the default iterator for an object. This symbol is used to define the behavior of thefor...ofloop and other built-in methods that iterate over objects.Symbol.toPrimitive: A well-known symbol that is used to define the behavior of an object when it is coerced to a primitive value (e.g., when it is used in an arithmetic operation or converted to a string).Symbol.toStringTag: A well-known symbol that is used to define the string representation of an object when it is converted to a string using theObject.prototype.toString()method.Symbol.hasInstance: A well-known symbol that is used to define the behavior of theinstanceofoperator for a constructor function.Symbol.species: A well-known symbol that is used to specify the constructor function that should be used to create derived objects (e.g., subclasses) when a built-in method returns a new object.
There are also several other built-in symbols, such as Symbol.isConcatSpreadable, Symbol.match, Symbol.replace, and Symbol.search, which are used to define the behavior of built-in methods for specific types of objects.
Comment if you have any doubts or suggestions on this Js data type topic.
Note: The All JS Examples codes are tested on the Firefox browser and the Chrome browser.
OS: Windows 10
Code: HTML 5 Version