Iterate over a JavaScript object

Iteration involves looping through the object's properties one by one. Depending on the method used, you can access and manipulate different levels of properties efficiently. Here are several methods.

[Approach 1]: Using for...in Loop

A for..in loop iterates over all enumerable properties of an object, including inherited ones. Use hasOwnProperty() to filter only the object’s own properties, and access each value using the key.

function iterateObject() {
    let exampleObj = {
        book: "Sherlock Holmes",
        author: "Arthur Conan Doyle",
        genre: "Mystery"
    };

    for (let key in exampleObj) {
        if (exampleObj.hasOwnProperty(key)) {
            value = exampleObj[key];
            console.log(key, value);
        }
    }
}
iterateObject();

book Sherlock Holmes
author Arthur Conan Doyle
genre Mystery

Syntax: 

for (let key in exampleObj) {    
if (exampleObj.hasOwnProperty(key)) {        
         value = exampleObj[key];        
         console.log(key, value);   
 }
}

[Approach 2]: Using Object.entries() and map()

Object.entries() returns an array of an object’s own enumerable key-value pairs. Use map() to access each pair, where index 0 is the key and index 1 is the value.

function iterateObject() {
    let exampleObj = {
        book: "Sherlock Holmes",
        author: "Arthur Conan Doyle",
        genre: "Mystery"
    };

    Object.entries(exampleObj).map(entry => {
        let key = entry[0];
        let value = entry[1];
        console.log(key, value);
    });
}
iterateObject();

book Sherlock Holmes
author Arthur Conan Doyle
genre Mystery

Syntax:

Object.entries(exampleObj).map(entry => {     
   let key = entry[0];     
   let value = entry[1];     
   console.log(key, value); 
});

[Approach 3]: Using forEach() and object.keys() Method

object.keys() Method returns an array of keys of the object and forEach() method is an array method that allows you to iterate over each element in the array.

function iterateObject() {
    let exampleObj = {
        book: "Sherlock Holmes",
        author: "Arthur Conan Doyle",
        genre: "Mystery"
    };

    Object.keys(exampleObj).forEach(key => {
        const value = exampleObj[key];
        console.log(`${key}: ${value}`);
    });

}
iterateObject();

book: Sherlock Holmes
author: Arthur Conan Doyle
genre: Mystery