There are several ways to iterate over an object’s properties in JavaScript.

Object.entries() returns an array of object’s own enumerable string-keyed property [key, value] pairs. This array can then be iterated over using forEach() or for…of.

Example

const book = {
  "title": "To Kill a Mockingbird",
  "author": "Harper Lee",
  "pages": 281
};

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

Output

title: To Kill a Mockingbird
author: Harper Lee
pages: 281

Similarly, for...of can also be used with Object.entries().

for (let [key, value] of Object.entries(book)) {
  console.log(`${key}: ${value}`);
}

for…in

for...in statement can also be used to iterate over object properties, but it also iterates over inherited properties. Luckily, hasOwnProperty() method can be used to check if a property is object’s own property.

const book = {
  "title": "To Kill a Mockingbird",
  "author": "Harper Lee",
  "pages": 281
};

for (let key in book) {
  if (book.hasOwnProperty(key)) {
    console.log(`${key}: ${book[key]}`);
  }
}

Object.keys() and Object.values()

If we are only concerned with object property keys, then Object.keys() can be used. Similarly, Object.values() can be used to get object property values.

const book = {
  "title": "To Kill a Mockingbird",
  "author": "Harper Lee",
  "pages": 281
};

Object.keys(book).forEach(key => {
  console.log(key);
});

Object.values(book).forEach(value => {
  console.log(value);
});