Why Do My React Array Children Need Unique Keys?

Understanding Unique Keys for Array Children in React.js

In React, it is important to assign unique keys to array children to optimize performance and avoid unnecessary re-rendering.

Issue:
You are receiving an error stating: "Each child in an array should have a unique 'key' prop" while rendering a sortable table using a JSON data source.

Investigation:

``

{rows}

``
``
var TableRowItem = React.createClass({
render: function() {

var td = function() {
  return this.props.columns.map(function(c) {
    return <td key={this.props.data[c]}>{this.props.data[c]}</td>;
  }, this);
}.bind(this);

return (<tr >{ td(this.props.item) }</tr>);

}
});
``

Solution:
The issue stems from the absence of unique keys for the elements rendered within the TableRowItem component.

To ensure that each child in the rows array has a unique key prop, you must add keys to the elements within the TableRowItem component as well.

var TableRowItem = React.createClass({
  render: function() {

    var td = function() {
      return this.props.columns.map(function(c) {
        return <td key={this.props.key + '-' + c}>{this.props.data[c]}</td>;
      }, this);
    }.bind(this);

    return (<tr >{ td(this.props.item) }</tr>);
  }
});

By adding unique keys to the elements, React can track individual elements and perform efficient updates, preventing unnecessary re-rendering of the entire row.

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