Loop through array of objects in React

Component reusability is one of the cornerstones of building web apps in React. Developers can write the component once and reuse it as many times as they need. Check SimpleFrontEnd for great tutorials on React.

Why we need to loop through array of objects

Often we need to render components based on data received from the API. External data can be formatted in many different ways. Most often, we receive an array of objects. Each object contains information to render a component or element. Most often, we use map(), filter(), or other array methods to return a new array with modified items. And the callback function is used to specify how every item needs to be modified.

However, looping through an array of objects requires some precision. First of all, let’s look at how to import an array of objects from an external source. This is usually done using the useEffect() hook. It’s important to understand how the dependency array works and how useEffect () can replace lifecycle hooks, typically used to perform side-effects in React.

Once you have an array of objects stored in a state variable, you can get to work. You need to create a new array where every item is an element or a component. Methods like map() and filter() are perfect for this purpose. Map() returns a new array made up of transformed components, and filter() does the same except it filters array items as well.

Using map() to loop through array of objects

So, how do you use map() to loop through array of objects in React? You take information contained in objects and use this information as values for props and contents for components.

You can create a new array of elements and components in JSX or outside of it. The latter option is better, because it’s more readable to separate JavaScript logic from JSX as much as possible. It’s better to finish the array transformation and store final result in a variable. Then you can reference that variable inside JSX. Remember to use curly braces to differentiate dynamic expressions from normal content in JSX.

If you do decide to use map() directly in the JSX, you will need to use curly braces. In fact, you might need to use curly braces on multiple levels. For example, you need initial curly braces to embed the initial expression (performing map() on array). Remember that map() callback function usually returns JSX, so you need to use curly braces again when you need to embed values from the object into elements.

There are other things to remember when you use map() to loop over objects in the array. For example, every new component or React element must have a unique id property. This is necessary so React can reliably identify every DOM element.

Technically, you can also use for loops and forEach to loop through an array of objects in React. However, doing this requires more lines of code and the end result simply isn’t as readable as using the map() method. SimpleFrontEnd explores different ways to loop through an array of objects in React.

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