JavaScriptObjects and classes
Object.
Freezes an object, blocking the addition, removal, and change of its properties.
- Returns
- The same object, now frozen.
- Changes the original
- Yes
Example
#JavaScript
const LEVELS = Object.freeze({ easy: 1, medium: 2, hard: 3 })
try {
LEVELS.easy = 5
} catch (error) {
console.log(error.name)
}
console.log(LEVELS.easy)
console.log(Object.isFrozen(LEVELS))Console
TypeError
1
true
Definition and usage
#The Object.freeze() method makes an object impossible to change further: you can’t add new properties, remove existing ones, or change their values. In strict mode, which is how modules run, any such attempt throws a TypeError.
It’s useful for configuration constants and lookup tables that shouldn’t be accidentally changed somewhere else in the program.
Freezing is shallow: nested objects can still be changed, unless you freeze them separately. Object.isFrozen() checks whether an object is frozen.
Syntax
#Syntax
Object.freeze(obj)Parameters
#obj
object
The object to freeze.
More examples
#JavaScript
const config = Object.freeze({ api: { timeout: 1000 } })
config.api.timeout = 5000
console.log(config.api.timeout)Console
5000
Browser support
#Widely available
Works in all modern browsers, phones included. You can use it without worry.
- Chrome
- Edge
- Firefox
- Safari
Good practices
#constonly protects the variable assignment. You needObject.freeze()to lock down the object’s contents.- For a deep freeze, you have to walk recursively through the nested objects.
Related entries
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