The entries() method of the JavaScript Object object is a powerful tool introduced in ES2017. It allows you to retrieve all the own properties of an object and returns them as an array of [key, value] pairs.
Usage
To understand how to use the entries() method, let’s consider a simple example. Suppose we have an object called person with the properties name and age:
const person = { name: 'Fred', age: 87 }
We can use the entries() method on the person object to retrieve an array containing all its properties:
Object.entries(person) // [['name', 'Fred'], ['age', 87]]
In this case, the entries() method returns [['name', 'Fred'], ['age', 87]], which is an array of [key, value] pairs corresponding to the own properties of the person object.
The entries() method can also be used with arrays. Consider the following example:
const people = ['Fred', 'Tony']
Using the entries() method on the people array, we get:
Object.entries(people) // [['0', 'Fred'], ['1', 'Tony']]
In this case, the entries() method returns [['0', 'Fred'], ['1', 'Tony']], which is an array of [key, value] pairs representing the indices and values of the people array.
Utilizing the entries() Method
One practical use of the entries() method is to count the number of properties an object contains. Since the entries() method returns an array, you can combine it with the length property of the array to get the desired count.
For example, let’s say we have an object called product with several properties:
const product = { name: 'iPhone', brand: 'Apple', category: 'Electronics' }
You can count the number of properties in the product object using the following code:
const propertyCount = Object.entries(product).length
console.log(propertyCount) // 3
In this case, the propertyCount variable will hold the value 3, as the product object has three properties.
By understanding and utilizing the entries() method, you can effectively access and manipulate the properties of objects and arrays in your JavaScript code.