Ever since they were introduced, map() and filter() have become great tools for any programmer writing JavaScript code. Since React and other front-end frameworks are based on JavaScript, you can use these two methods in React as well.

In this article, we will discuss use cases for map() and filter() in React. Let’s start with the former.

React applications often receive data from an external API. When you need to display multiple components of the same type, data is usually formatted as array of objects. Each object describes an instance of a certain item. For example, an ecommerce website might receive an array of objects, where each object contains information about each product that needs to be displayed.

In these cases, you need to loop through an array of objects in React. map() is a great function to do just that. The method takes one argument – a callback function.

When you call map() on a certain array, it runs a callback function on every item in the array, then stores each of these items in a new array. You can use this functionality of map() to take objects in the array, and return JSX elements with specific attributes. You can get values from objects and use those values as contents or parameters of the JSX element.

JSX even allows you to embed a call to the map() function right in your code. JSX is nothing but JavaScript code disguised as HTML. Simply use curly braces to write JavaScript expressions within JSX. That way, the templating language will know that a certain part of your code should be evaluated as a JavaScript expression, not a normal content of the page.

React web developers often use map() to create JSX elements, or even separate components based on array of objects. It is a great way to automatically generate elements for every piece of data in the array.

Next is the filter() function. It works similarly to map(), with one big difference. It takes a callback function that returns a condition. The filter() function checks every item in the array against that condition, and creates a new array with items that met the condition. Therefore it is commonly used when you want to conditionally display elements and components for some items in the array.

To use filter() in JSX, you should follow similar rules to map().  You can embed it directly in JSX, but need to wrap the code with curly braces. You need the filter() method to conditionally loop through an array of objects in React.

In conclusion, these two functions are very useful for working with external data in React. You can use both map() and filter() methods to create elements from an array of objects. You take information from objects, and use it as content or attributes for components.