JavaScript Object entries() Method

The Object.entries() method in JavaScript is used to retrieve an array of an object's enumerable property [key, value] pairs. This method is particularly useful for transforming and iterating over objects in situations where array-like manipulation is needed.

Syntax:

Object.entries(obj);

Parameters:

• obj: It is the object whose enumerable property [key, value] pairs are to be returned.

Return Value:

Object.entries() returns an array consisting of enumerable property [key, value] pairs of the object passed.

Key Characteristics

• The order of the properties returned by Object.entries() is the same as the order provided by manually iterating over the properties of the object.
• It only returns enumerable properties that belong to the object directly (not inherited from its prototype chain).

Examples of JavaScript Object entries() Method

Example 1: In this example, an object "obj" has been created with three property[key, value] pairs, and the Object.entries() method is used to return the first property [key, value] pair of the object.

// Creating an object constructor
// and assigning values to it
const obj = { 0: 'adam', 1: 'billy', 2: 'chris' };
    
// Displaying the enumerable property [key, value]
// pairs of the object using object.entries() method
console.log(Object.entries(obj)[1]);

[ '1', 'billy' ]

Example 2: In this example, an object "obj" has been created with three property[key, value] pairs, and the Object.entries() method is used to return all the property [key, value] pairs of the object. 

// Creating an object constructor and
// assigning values to it
const obj = { 10: 'adam', 200: 'billy', 35: 'chris' };

// Displaying the enumerable property [key, value]
// pairs of the object using object.entries() method
console.log(Object.entries(obj));

[ [ '10', 'adam' ], [ '35', 'chris' ], [ '200', 'billy' ] ]

Applications of Object.entries()

Iterating over Objects:

You can easily iterate over the object’s properties by using Object.entries() in combination with array methods like forEach() or map().

const obj = { name: 'Alice', age: 25, city: 'New York' };
Object.entries(obj).forEach(([key, value]) => {
    console.log(`${key}: ${value}`);
});

name: Alice
age: 25
city: New York

Converting Objects to Arrays:

Since Object.entries() returns an array of arrays, it is useful for converting objects into arrays, especially when you need to work with array-specific functions.

const obj = { name: 'Alice', age: 25, city: 'New York' };
const entries = Object.entries(obj);
console.log(entries);

[ [ 'name', 'Alice' ], [ 'age', 25 ], [ 'city', 'New York' ] ]

Transforming Objects:

You can use Object.entries() to manipulate or transform an object, such as changing its structure or reformatting it.

const obj = { name: 'Alice', age: 25, city: 'New York' };
const transformed = Object.entries(obj).map(([key, value]) => [key.toUpperCase(), value]);
console.log(transformed);

[ [ 'NAME', 'Alice' ], [ 'AGE', 25 ], [ 'CITY', 'New York' ] ]

Handling Arrays:

Since arrays are objects in JavaScript, Object.entries() can be applied to arrays to get index-value pairs.

const arr = ['Apple', 'Banana', 'Cherry'];
const arrEntries = Object.entries(arr);
console.log(arrEntries);

[ [ '0', 'Apple' ], [ '1', 'Banana' ], [ '2', 'Cherry' ] ]

Handling Non-Enumerable Properties

The Object.entries() method only includes enumerable properties in the returned array. Non-enumerable properties (properties defined with Object.defineProperty() and the enumerable: false option) will not be included.

const obj = { name: 'Alice' };
Object.defineProperty(obj, 'age', {
    value: 25,
    enumerable: false
});

console.log(Object.entries(obj)); 

[ [ 'name', 'Alice' ] ]

Supported Browsers:

• Chrome
• Edge
• Firefox
• Opera
• Safari