Hash Tables & JavaScript Objects

const obj = {};
Object.preventExtensions(obj);
obj.newProp = 'test';
obj.existingProp = 'value';

Prevents value changes
Prevents property deletion
Prevents new properties
preventExtensions restricts object modification by: 1) Preventing addition of new properties, 2) Allowing modification of existing properties, 3) Allowing deletion of existing properties, 4) Cannot be reversed once applied, 5) Useful for controlling object structure, 6) Less restrictive than Object.freeze(), 7) Common in API design for interface stability, 8) Important for object immutability patterns.
Prevents all modifications