JavaScript const
Constant Array:
// Create an array:
const cars = ["Saab", "Volvo", "BMW"];
// Change an element:
cars[0] = "Toyota";
// Add an element:
cars.push("Audi");
Try it Yourself »
const cars = ["Saab", "Volvo", "BMW"];
// Change an element:
cars[0] = "Toyota";
// Add an element:
cars.push("Audi");
Constant Object:
// Create an object:
const car = {type:"Fiat", model:"500", color:"white"};
// Change a property:
car.color = "red";
// Add a property:
car.owner = "Johnson";
Try it Yourself »
const car = {type:"Fiat", model:"500", color:"white"};
// Change a property:
car.color = "red";
// Add a property:
car.owner = "Johnson";
Description
The const statement declares a variable.
Variables are containers for storing information.
Creating a variable in JavaScript is called "declaring" a variable:
const name = "Volvo";
Note
A const variable must be assigned when it is declared.
See Also:
JavaScript Reference: JavaScript var
JavaScript Reference: JavaScript let
Tutorials:
JavaScript Tutorial: JavaScript Variables
JavaScript Tutorial: JavaScript const
JavaScript Tutorial: JavaScript let
JavaScript Tutorial: JavaScript Scope
Syntax
const name = value;
Parameters
Parameter
Description
name
Required.
The name of the variable.
Variable names must follow these rules:
Must begin with a letter, or ,ドル or _
Names are case sensitive (y and Y are different)
Reserved JavaScript words cannot be used as names
The name of the variable.
Variable names must follow these rules:
Must begin with a letter, or ,ドル or _
Names are case sensitive (y and Y are different)
Reserved JavaScript words cannot be used as names
value
Required.
A value to be assigned to the variable.
A value to be assigned to the variable.
When to use JavaScript const?
As a general rule, always declare a variable with const unless you know that
the value will change.
Use const when you declare:
- A new Array
- A new Object
- A new Function
- A new RegExp
Browser Support
const is supported in all modern browsers:
| Chrome | Edge | Firefox | Safari | Opera | IE |
| Yes | Yes | Yes | Yes | Yes | 11 |
const is an ECMAScript6 (ES6 - JavaScript 2015) feature.