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

JavaScript Object static methods are some of the most powerful tools in the language — yet many developers use only Object.keys() and Object.assign(). Object.freeze() for immutability, Object.create() for prototype control, Object.fromEntries() for converting Maps — these unlock elegant solutions to common problems.

⚡ TL;DR: Object.keys/values/entries for iteration. Object.assign for shallow merge. Object.freeze for immutability. Object.create(null) for hash maps without prototype. Object.fromEntries converts [key,value] pairs back to object. Object.hasOwn replaces hasOwnProperty.

Iteration methods

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)
);

Object.assign — shallow merge

// 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};

Object.freeze — immutability

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 — prototype control

// 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

• ✅ Object.fromEntries after transforming .entries()
• ✅ Object.hasOwn(obj,key) over obj.hasOwnProperty(key)
• ✅ Object.freeze for config constants
• ✅ Object.create(null) for safe hash maps
• ❌ Object.assign is shallow — nested objects share reference
• ❌ Object.freeze is shallow — nested objects still mutable

External reference: MDN Object documentation.