How To Iterate Over A JavaScript Object

How to Iterate Over a JavaScript Object

In this post, we will give you information about How to Iterate Over a JavaScript Object. Here we will give you detail about How to Iterate Over a JavaScript Object And how to use it also give you a demo for it if it is necessary.

Suppose you have a simple JavaScript object:

const obj = {
  name: 'Luke Skywalker',
  title: 'Jedi Knight',
  age: 23
};

How do you iterate over the key/value pairs and print out “name: Luke Skywalker”, “title: Jedi Knight”, and “age: 23”? There are a lot of ways to do this in modern JavaScript. Here’s 3 different ways:

Using `Object.entries()`

The Object.entries() function returns an arrau coontaining the object’s key/value pairs. Here’s how you would print out
the key/value pairs using Object.entries() and a for/of loop.

const obj = {
  name: 'Luke Skywalker',
  title: 'Jedi Knight',
  age: 23
};

// Prints out:
// 'name: Luke Skywalker'
// 'title: Jedi Knight'
// 'age: 23'
for (const [key, value] of Object.entries(obj)) {
  console.log('${key}: ${value}');
}

In JavaScript, an entry is an array with exactly 2 elements, where the first element is the key and the second element is the value.
The entry pattern shows up in several other places in JavaScript, like the Map constructor and Object.fromEntries().

If you convert the iterator that Object.entries() returns into an array using Array.from(), you’ll get an array containing the object’s
key/value pairs.

const obj = {
  name: 'Luke Skywalker',
  title: 'Jedi Knight',
  age: 23
};

const keyValuePairs = Object.entries(obj);
keyValuePairs[0]; // ['name', 'Luke Skywalker']
keyValuePairs[1]; // ['title', 'Jedi Knight']
keyValuePairs[2]; // ['age', 23]

Using `Object.keys()`

The Object.keys() function returns an array of the object’s keys, as opposed to both the keys and the values. You can then use square brackets [] to get the object’s values.

const obj = {
  name: 'Luke Skywalker',
  title: 'Jedi Knight',
  age: 23
};

// Prints out:
// 'name: Luke Skywalker'
// 'title: Jedi Knight'
// 'age: 23'
for (const key of Object.keys(obj)) {
  console.log('${key}: ${obj[key]}');
}

Why use Object.keys() versus Object.entries()? Because you can’t change the value in an entry to change the value in the
object.

const obj = {
  name: 'Luke Skywalker',
  title: 'Jedi Knight',
  age: 23
};

// Assigning to 'value' does **not** change the property
// value! You need to do 'obj[key] = newValue'
for (let [key, value] of Object.entries(obj)) {
  if (key === 'title') {
    value = 'Jedi Master';
  }
}
obj.title; // 'Jedi Knight'

// Works!
for (const key of Object.keys(obj)) {
  if (key === 'title') {
    obj[key] = 'Jedi Master';
  }
}

With `for/in`

The Object.keys() and Object.entries() functions only loop over an object’s own properties. For a POJO, this distinction doesn’t matter. But when you use inheritance, this distinction can be important.

Using a for/in loop lets you iterate over all an object’s keys, including inherited keys.

function JediKnight(name, age) {
  this.name = name;
  this.age = age;
}
// 'title' is an inherited property for instances of the
// 'Jedi Knight' class.
JediKnight.prototype.title = 'Jedi Knight';

const obj = new JediKnight('Luke Skywalker', 23);

// 'entries' will **not** include the 'title' property
const entries = Object.entries(obj);
entries; // [['name', 'Luke Skywalker'], ['age', '23']]

// Includes 'title', because 'for/in' also loops over
// inheritted properties.
// 'name: Luke Skywalker'
// 'age: 23'
// 'title: Jedi Knight'
for (const key in obj) {
  console.log('${key}: ${obj[key]}');
}

Generally speaking, you should use Object.keys() or Object.entries()with POJOs to avoid accidentally picking up inheritted properties. But you can use for/in if you’re sure you want to loop over inheritted properties.

JavaScript Fundamentals for How to Iterate Over a JavaScript Object

JavaScript is a programming language that is used to create interactive web pages. It is a client-side scripting language, which means that it runs on the user’s browser. JavaScript can be used to add animation, interactivity, and functionality to web pages.

Here are some of the fundamentals of JavaScript:

Variables: Variables are used to store data. They are declared using the var keyword.
Data types: JavaScript has a variety of data types, including strings, numbers, booleans, objects, and arrays.
Operators: Operators are used to perform operations on data.
Control flow statements: Control flow statements allow you to control the order in which your code is executed.
Functions: Functions are blocks of code that can be reused.
Objects: Objects are used to store data in key-value pairs.
Arrays: Arrays are used to store data in a sequential order.
Events and event handlers: Events are notifications that are sent by the browser when something happens, such as when the user clicks on an element or moves the mouse over an element. Event handlers are functions that are called in response to an event.
DOM manipulation: The Document Object Model (DOM) is a tree-like structure that represents the elements of a web page. JavaScript can be used to manipulate the DOM to change the appearance or behavior of a web page.

These are just some of the fundamentals of JavaScript. There are many other concepts that you can learn as you continue to develop your skills.

Here are some resources that you can use to learn more about JavaScript:

Mozilla Developer Network (MDN): The MDN is a great resource for learning about JavaScript. It has a comprehensive reference guide, tutorials, and articles on a wide range of topics.
W3Schools: W3Schools is another great resource for learning about JavaScript. It has interactive tutorials and quizzes that can help you learn the basics of the language.
JavaScript.info: JavaScript.info is a website that provides in-depth tutorials on JavaScript. It also has a forum where you can ask questions and get help from other JavaScript developers.

I hope this helps for How to Iterate Over a JavaScript Object!

Here are some additional tips for learning JavaScript:

Start with the basics: Before you start trying to build complex applications, it’s important to learn the basics of JavaScript. This includes things like variables, data types, operators, and control flow statements.
Practice regularly: The best way to learn JavaScript is to practice regularly. Try to find some time each day to work on JavaScript projects.
Get help from others: If you get stuck, don’t be afraid to ask for help from others. There are many online forums and communities where you can get help from other JavaScript developers.

With a little practice, you’ll be able to learn JavaScript and start building amazing web applications.

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