Understanding unique keys for array children in React.js

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In the context of React development, many components are notable mentions. One factor that you might have heard about related to React.js is array children. It is highly useful for React-based software development, so first understanding them is vital.

If you are finding remote React programmer to create a new application, take the help of certified experts from Bosc Tech Labs. But first, learn the details on what children and unique keys mean in React.

What do children mean in React?

In React, the term ‘children’ is related to a generic box that contains hidden content until it passes through the parent coding component. Developers invoke the component from an App component typically. So, when the component is invoked, the main content appears within the opening/closing tags.

The children in React.Js have a variety of uses and can turn into different things. There are valuable for situations like:

  • The need for a wrapper in nested structures.
  • The elements are unknown.
  • One can group multiple similar elements together to form one parent element.

To note, if there is a need for the same children in different components, you can assign them to render with specific variables. After that, pass them as children.

Why is it important to under the keys related to array children?

It is important to stay vigilant and operate carefully while carrying our array-based iterations. Many assume that operating the element-related index within the React array is useful for avoiding familiar issues or errors in the coding. There is a belief that all array children should hold unique keys.

While that applies to some props.children, it is not a universal rule. Typically, this falls under the category of an anti-pattern. This can result in unwanted behavior in specific situations.

What are key props?

To emphasize, React utilizes key props for understanding the relation between component-to-DOM elements. These are useful in the reconciliation sequence. Thus, it is important to keep all keys unique for React to recognize and mutate the right elements.

Similarly, the unique React key props should stay static during the rerendering process for a better performance guarantee. While it is better to follow these rules for the key props usage in reconciliation, it can be avoided in certain cases as long as the array’s static nature is confirmed.

So, essentially, key props should be:

  • Static- not changing at all between renders.
  • Unique- not identical to their sibling component

Some experts say keys are not always performance quality indicators but are mainly about identification. It is not always simple to know the data model, and providing automatic keys is difficult for most coders to avoid major errors.

It is better to utilize a hashing function, as some of the best developers are trained. This approach makes it easier and safer to carry out the components rerendering with no ids in place.

How to use key props?

To properly understand the usage process for Key props, you should take the right approach in different situations. For example, here are some examples.

Example 1: Bad

    {rows.map((row) => {
        return <ObjectRow key={Math.random()} />;


Unique keys are guaranteed with this approach. However, React makes development faster as it would rerender all items within the list without any choice. It has no control over choosing to render an item even if it does not require rerendering.

Therefore, the performance of the component would suffer. Additionally, experts cannot eliminate the worry of a key collision during a key collision in specific events with unstable keys. That would result in the growth of more DOM nodes and component instances, and that would cause array children to lose state.

Example 2:Potentially Bad

    {rows.map((row, i) => {
        return <ObjectRow key={i} />;


This type of array-based iteration in React app development is risky for most developers to handle with guaranteed success. It is effective if the iteration is via a static array type. But if you have to remove, add, filter, or reorder any items, it is important to proceed cautiously to avoid this common mistake.

Typically, static keys like “Products” or “Home” require no changes or new links. So, they are safe to use with this approach. Plus, if your array is used as LIFO or stack format and is not filtered/reordered, it is safe to use and carry out this key. So, it is not entirely harmful.

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Example 3: Usable

componentWillMount() {
  let rows = this.props.rows.map(item => { 
    return {uid: SomeLibrary.generateUniqueID(), value: item};


    {rows.map((row) => {
        return <ObjectRow key={row.uid} />;


Key collisions are possible if the dataset holds no unique data like array children full or arbitrary numbers. You can manually create unique identifiers for all dataset items before the iteration. This way, it is easier to handle than carrying out the approach for all rerendering phases.

Example 4: Highly Suitable

            list.map(({ key, value }) => 
) )


Many expertise prefer this approach since it works with unique keys for every dataset item. Developers can operate with the Primary key from the table easily for rerendering.

You can use data IDs as keys or, choose a string that contains one of the identified list items as a sibling component.

var data = [{name:'Oliver', age:20, city:'HO'},
            {name:'Erika ', age:34, city:'HN'},
            {name:'Theresa', age:24, city:'IT'}

var Hello = React.createClass({
    render: function() {
      var _data = this.props.info;
            {_data.map(function(object, i){
               return <div className={"row"} key={i}> 
                          {[ object.name ,
                             <b key={i}> {object.city} </b> , 
React.render(<Hello info={data} />, document.body);


Overall, unique keys are essential to consider while working with React. Js-based array children. Follow the processes mentioned for specific situations, depending on the availability of IDs and component details.

For your business’s next react app development project, get in touch with us! We have worked on various projects and handled issues with correct and perfect solutions. Reach out and discuss your requirements.

Frequently Asked Questions (FAQs)

1. What is the wrapper component in React development?

A wrapper component has unknown components and offers the default structure to view the child components.

2. What are the props in React app development?

Props are utilized to pass data from one component to another, i.e., from parent to child components, as these props are helpful when you wish the data flow in your application to stay dynamic.

3. What is re-rendering in ReactJS?

Re-render occurs when React requires updating the application with the latest and new data. Mostly, it happens when the user interacts with an app or a few external data via the asynchronous request or a subscription model.

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