JavaScript Object Methods: Object.keys, assign, freeze, create and More

const user = {name:'Alice',age:30,role:'admin'};
Object.keys(user)    // ['name','age','role']
Object.values(user)  // ['Alice',30,'admin']
Object.entries(user) // [['name','Alice'],['age',30],['role','admin']]

// Transform all values:
const doubled = Object.fromEntries(
  Object.entries(scores).map(([k,v])=>[k,v*2])
);

// Filter object by value:
const passing = Object.fromEntries(
  Object.entries(grades).filter(([,v])=>v>=60)
);

// Merge objects (left to right, last wins)
const config = Object.assign({}, defaults, userConfig);
// Copies enumerable own properties
// SHALLOW: nested objects still shared reference

// Spread alternative (same behavior):
const merged = {...defaults, ...userConfig};

// Clone (shallow):
const clone = Object.assign({}, original);
const clone2 = {...original};

const config = Object.freeze({
  API_URL: 'https://api.example.com',
  TIMEOUT: 5000
});
config.API_URL = 'hacked'; // Silent failure in sloppy, TypeError in strict
config.NEW = 'value';     // Silently ignored

// Deep freeze:
const deepFreeze = obj => {
  Object.keys(obj).forEach(k => {
    if(typeof obj[k]==='object' && obj[k]!==null) deepFreeze(obj[k]);
  });
  return Object.freeze(obj);
};

// Object.create(null) = hash map with no prototype
const safeMap = Object.create(null); // No __proto__, toString, etc.
safeMap['key'] = 'value'; // Safe for any key

// Object.create(proto) = set prototype
const animal = { breathe() { return 'breathing'; } };
const dog = Object.create(animal);
dog.bark = ()=>'woof';
dog.bark();    // 'woof' — own
dog.breathe(); // 'breathing' — from prototype