To loop through an object in JavaScript, use for...in with hasOwnProperty(), Object.keys/values/entries, or Reflect.ownKeys() depending on needs. 1. Use for...in to iterate over enumerable string properties, but always check with hasOwnProperty() to skip inherited properties. 2. Use Object.keys(), Object.values(), or Object.entries() to get arrays of keys, values, or key-value pairs, enabling array methods like .map() and .forEach(). 3. Use Reflect.ownKeys() when needing all keys including non-enumerable and symbol types, useful for debugging or meta-programming. These methods offer varying levels of control and specificity for different use cases.

When you need to loop through an object in JavaScript, there are several solid options available. None of them are overly complicated, but choosing the right one depends on what exactly you're trying to do — whether it's just accessing keys, values, or both.

Using for...in Loop

This is one of the most common ways to iterate over object properties. It loops through the enumerable string properties of an object, which includes those inherited through the prototype chain.

const user = {
  name: 'Alice',
  age: 25,
  role: 'developer'
};

for (let key in user) {
  console.log(key   ': '   user[key]);
}

Be aware though — if someone adds properties to the prototype of Object, your loop might pick those up too. To avoid that, always use hasOwnProperty():

• Check with user.hasOwnProperty(key) before doing anything inside the loop.

Also note that the order isn't guaranteed for non-integer keys, so don’t rely on it unless you’re using ES2015 and only dealing with string keys.

Get Keys or Values with Object.keys, Object.values, Object.entries

If you want more control and cleaner syntax, these methods are modern and widely supported.

• Object.keys(obj) returns an array of the object’s own enumerable keys.
• Object.values(obj) gives you an array of the values.
• Object.entries(obj) returns an array of [key, value] pairs.

They all let you use array methods like .map(), .forEach(), etc., which can be more convenient than a plain loop.

Object.entries(user).forEach(([key, value]) => {
  console.log(`${key}: ${value}`);
});

One thing to remember: these methods don’t include inherited properties. That’s usually a good thing unless you specifically need to go up the prototype chain.

Use Reflect.ownKeys() for More Control

If you ever need to get all keys of an object — including non-enumerable and symbol keys — this method has you covered.

const obj = {
  regularKey: 'hello'
};

Object.defineProperty(obj, 'secret', {
  value: 42,
  enumerable: false
});

console.log(Reflect.ownKeys(obj)); // ["regularKey", "secret"]

It doesn’t care about enumerability or type — it just lists everything directly on the object. You won’t use this every day, but it's useful when debugging or working with meta-programming.

That's basically it. For most everyday tasks, for...in with a hasOwnProperty check or Object.entries() should cover your needs. The others come in handy when you need something more specific or precise.

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