Finding the length of a JavaScript object

JavaScript objects don't have a built-in length property like arrays. However, there are several methods to find the number of properties in an object.

Suppose we have an object like this:

const obj = {
  name: "Ramesh",
  age: 34,
  occupation: "HR Manager",
  address: "Tilak Nagar, New Delhi",
  experience: 13
};

We need to count the number of properties in this object.

Using Object.keys() (Recommended)

The most common and reliable method is Object.keys(), which returns an array of the object's property names:

const obj = {
  name: "Ramesh",
  age: 34,
  occupation: "HR Manager",
  address: "Tilak Nagar, New Delhi",
  experience: 13
};

const length = Object.keys(obj).length;
console.log("Object length:", length);

Object length: 5

Using for...in Loop

You can manually count properties using a for...in loop with hasOwnProperty() to ensure you only count the object's own properties:

const obj = {
  name: "Ramesh",
  age: 34,
  occupation: "HR Manager",
  address: "Tilak Nagar, New Delhi",
  experience: 13
};

function getObjectLength(obj) {
  let count = 0;
  for (let key in obj) {
    if (obj.hasOwnProperty(key)) {
      count++;
    }
  }
  return count;
}

console.log("Object length:", getObjectLength(obj));

Object length: 5

Using Object.entries()

Object.entries() returns an array of key-value pairs, so its length gives us the property count:

const obj = {
  name: "Ramesh",
  age: 34,
  occupation: "HR Manager"
};

const length = Object.entries(obj).length;
console.log("Object length:", length);
console.log("Entries:", Object.entries(obj));

Object length: 3
Entries: [ [ 'name', 'Ramesh' ], [ 'age', 34 ], [ 'occupation', 'HR Manager' ] ]

Comparison

Edge Cases

Be aware that these methods only count enumerable own properties:

const obj = {};
Object.defineProperty(obj, 'hidden', {
  value: 'secret',
  enumerable: false
});

obj.visible = 'public';

console.log("Keys count:", Object.keys(obj).length);
console.log("Keys:", Object.keys(obj));

Keys count: 1
Keys: [ 'visible' ]

Conclusion

Use Object.keys(obj).length as the standard way to find an object's property count. It's concise, readable, and performs well for most use cases.