Object.freeze

Examples

Changes are silently ignored:

const config = Object.freeze({ port: 3000 });
 
config.port = 8080;
config.host = 'localhost';
 
console.log(config);

Output:

{
  "port": 3000
}

In strict mode (in modules and classes) a change throws an error:

'use strict';
const config = Object.freeze({ port: 3000 });
 
try {
  config.port = 8080;
} catch (error) {
  console.log(error.name);
}

Output:

TypeError

Notes

Freezing is shallow: nested objects can still change unless you freeze them too.

const and Object.freeze() are different: const forbids assigning another object to the variable, freeze forbids changing the object itself.