JavaScript Object Methods CheatSheet (Quick Reference)

If you only save one page for JavaScript objects — make it this one.

📚 Official Docs: MDN Docs

📌 Index

1. Object.keys()
2. Object.values()
3. Object.entries()
4. Object.fromEntries()
5. Object.assign()
6. Object.hasOwn()
7. Object.freeze()
8. Object.seal()
9. Object.create()
10. Object.getPrototypeOf()

🚀 Methods Explained

1. Object.keys()

What it does: Returns all keys of an object

Example:

Object.keys({ a: 1, b: 2 });

Output:

["a", "b"]

2. Object.values()

What it does: Returns all values of an object

Example:

Object.values({ a: 1, b: 2 });

Output:

[1, 2]

3. Object.entries()

What it does: Returns key-value pairs as arrays

Example:

Object.entries({ a: 1, b: 2 });

Output:

[["a", 1], ["b", 2]]

4. Object.fromEntries()

What it does: Converts entries back to object

Example:

Object.fromEntries([["a", 1], ["b", 2]]);

Output:

{ a: 1, b: 2 }

5. Object.assign()

What it does: Merges objects (shallow copy)

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Example:

Object.assign({}, { a: 1 }, { b: 2 });

Output:

{ a: 1, b: 2 }

6. Object.hasOwn()

What it does: Checks if property exists (own property only)

Example:

Object.hasOwn({ a: 1 }, "a");

Output:

true

7. Object.freeze()

What it does: Prevents any changes to the object

Example:

const obj = Object.freeze({ a: 1 });
obj.a = 2;

Output:

{ a: 1 } // unchanged

8. Object.seal()

What it does: Allows updating values but prevents adding/removing keys

Example:

const obj = Object.seal({ a: 1 });
obj.a = 2;
obj.b = 3;

Output:

{ a: 2 } // 'b' not added

9. Object.create()

What it does: Creates a new object with a given prototype

Example:

const proto = { a: 1 };
const obj = Object.create(proto);

obj.a;

Output:

1

10. Object.getPrototypeOf()

What it does: Returns the prototype of an object

Example:

Object.getPrototypeOf({});

Output:

Object.prototype

🎯 Quick Mental Model

• keys() → keys
• values() → values
• entries() → key + value
• fromEntries() → reverse
• assign() → merge
• freeze() → lock
• seal() → partial lock

🔥 Pro Tips

• Prefer Object.hasOwn() over hasOwnProperty() ✅
• Use entries → map → fromEntries for transformations 🚀
• Object.assign() is shallow copy ⚠️
• Use Object.freeze() for constants