Unique “key” prop warning in render method - ReactJS

Question

My app have a warning say that: Each child in an array or iterator should have a unique "key" prop. Check the render method of 'SortableTable' Each child in an array or iterator should have a unique "key" prop. Check the render method of 'SortableTable' Hear is my SortableTable file:

import React from 'react';
import {Link} from 'react-router';
import {v4 as uuid} from 'node-uuid';

export default class SortableTable extends React.Component {
    render() {

        return (
            <table style={{width: '100%'}} className={this.props.className} id={this.props.id}>
                <thead>
                    <tr>
                        {this.props.headers.map(this.generateHeaders)}
                    </tr>
                </thead>
                <tbody>
                    {this.props.children}
                </tbody>
            </table>
        );
    }

    generateHeaders = (value) => {
        if (Object.keys(value).length === 0) return
        let sort, colspan
        if(value.sort) {

            let {query} = this.props;
            let nQuery, title, icon, colspan = 1;
            if(query.sort === value.sort && query.sortDirection === 'desc') {
                nQuery = Object.assign({}, query, {sort: value.sort, sortDirection: 'asc', page: 1})
                title = 'asc';
                icon = String.fromCharCode(0xe630)
            } else {
                nQuery = Object.assign({}, query, {sort: value.sort, sortDirection: 'desc', page: 1})
                title = 'desc';
                icon = String.fromCharCode(0xe62d)
            }
            sort = <Link to={this.props.link} query={nQuery} className="icon order active" title={title} data-icon={icon} />

        }
        let className = value.className ? value.className : ''
        if(value.colspan) {
            colspan = value.colspan
        }
        return <th className={className} colSpan={colspan}><span>{value.name}</span>{sort}</th>
    }

Can someone show me how to set key prop to resolve this warning?

Answer 1

The idea is to have a key attribute with a unique value. You can use index, the second argument of Array#map callback :

generateHeaders = (value, index) => {
    // ...
    return <th key={index} className={className} colSpan={colspan}><span>{value.name}</span>{sort}</th>
}

Alternatively, if value object has a unique property like id , you may use it instead.

Answer 2

The <th> element returned by generateHeaders needs to have a key attribute set on it, since you're returning an array of them from your render method.

The simplest way to achieve this is to use the index:

generateHeaders = (value, index) => {
// ...
    return <th key={index} //...

This will make the warning go away but it's better to use a unique property of each value , if one exists. This is because React uses the key to determine whether two items are the same. If you're using the array index and you insert a new value somewhere into the array, the indexes will change, causing the items to be re-rendered unnecessarily.

Answer 3

您应该将密钥插入标签：

generateHeaders = (value, index) => { ... return <th key={index} className={className} colSpan={colspan}><span>{value.name}</span>{sort}</th> }