How do I loop through or enumerate a JavaScript object?

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byAlex Kataev·Feb 12, 2025

To enumerate properties in a JavaScript object, use the for...in loop:

const obj = { a: 1, b: 2, c: 3 };
for (const key in obj) {
  // Check "if key has key!" Hmm, grammar, eh?
  if (obj.hasOwnProperty(key)) {
    console.log(`${key}: ${obj[key]}`);
  }
}

Be sure to use obj.hasOwnProperty(key) to skip inherited properties and ensure you're only focusing on the object's unique properties.

Taking things up a notch: Cleaner iteration methods

Embrace the power of `Object.keys()`, `Object.values()`, and `Object.entries()`

For cleaner and more manageable code, utilize these modern JavaScript methods. They make enumeration a breeze:

const obj = { a: 'Hello', b: 'Stack', c: 'Overflow' };

// "A key to success: Find keys!"
for (const key of Object.keys(obj)) {
  console.log(`${key}: ${obj[key]}`);
}

// "Values are not just numbers anymore!"
for (const value of Object.values(obj)) {
  console.log(value);
}

// "It takes two to make a thing go right: [key, value]!"
for (const [key, value] of Object.entries(obj)) {
  console.log(`${key}: ${value}`);
}

Hunting for elusive Symbols and non-enumerable properties

Symbols and non-enumerable properties - they won't show up in your usual for...in loop or Object.keys(). Here's how to catch them:

const symbolKey = Symbol('unique');
const newObj = { [symbolKey]: 'symbolValue', hidden: 'invisible' };
Object.defineProperty(newObj, 'hidden', { enumerable: false });

// "Symbol hunting season is open!"
console.log(Object.getOwnPropertySymbols(newObj)); // Output: [Symbol(unique)]
console.log(Object.getOwnPropertyNames(newObj)); // Output= ['hidden']

Library to the rescue: Lo-Dash and Underscore.js

Feel like for...in is too mainstream? Shake things up with utility libraries like Lo-Dash or Underscore.js:

// "Lo-Dash: An underscore on steroids!"
_.forEach(discoBall, (value, key) => {
    console.log(key + ' Disco ' + value);
});

// Are you my own property or an imposter? Check with _.forOwn
_.forOwn(discoBall, (value, key) => {
    console.log('Retro ' + key + ': ' + value);
});