How to get the length of a JavaScript object?

To get the length (number of properties) of a JavaScript object, you can use one of these methods:

1. Using Object.keys() (ES6+ Recommended)

Convert the object’s keys to an array and get its length:

const obj = { a: 1, b: 2, c: 3 };
const length = Object.keys(obj).length; // 3

2. Using a Loop (Legacy Approach)

Loop through the object’s properties and count them:

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

const obj = { x: 10, y: 20 };
console.log(getObjectLength(obj)); // 2

3. Using Object.getOwnPropertyNames() (Includes Non-Enumerable Properties)

Get all own properties (even non-enumerable ones):

const obj = Object.create({}, {
  a: { value: 1, enumerable: true },
  b: { value: 2, enumerable: false }
});

const length = Object.getOwnPropertyNames(obj).length; // 2

Key Notes:

• Object.keys() returns only enumerable own properties.
• for...in loops include inherited enumerable properties unless filtered with hasOwnProperty.
• Object.getOwnPropertyNames() includes all own properties (enumerable and non-enumerable).
• Symbol keys are ignored in all methods above. Use Object.getOwnPropertySymbols() to include them:

  const sym = Symbol('key');
  const obj = { [sym]: 'value', a: 1 };
  const totalKeys = Object.keys(obj).length + Object.getOwnPropertySymbols(obj).length; // 2

Edge Cases:

• If the object is null or undefined, wrap it in a check:

  const obj = null;
  const length = obj ? Object.keys(obj).length : 0; // 0

Example Workflow:

const user = { name: "Alice", age: 30, role: "Admin" };
console.log(Object.keys(user).length); // 3

// Add a non-enumerable property
Object.defineProperty(user, 'id', { value: 123, enumerable: false });
console.log(Object.keys(user).length); // 3 (still)
console.log(Object.getOwnPropertyNames(user).length); // 4

Use Object.keys() for most cases, and fall back to loops or Object.getOwnPropertyNames() for specialized scenarios.