这是我的 React 组件

import React, { Component } from 'react';
import categories from './categories.json'
import './content.css'

export default class Content extends Component {
    constructor(props) {
        super(props)
        this.state = {
            searchText: '',
            categories
        }
    }

    render() {
        return(
            <div className="content">
            <form className="searchform" onSubmit={this.search}>
                <input type="text" name="keyword" id="searchbox" placeholder="Search String"></input>
                <select name="categories" id="searchcategories">
                <option defaultValue="" defaultChecked>Select a category</option>
                {this.state.categories.map(x => 
                    <option key={x.value} value={x.value}>{x.name}</option>
                )}</select>
                <input type="submit" value ="Search" id="searchsubmit" />
            </form>
            </div>
        )
    }

    search(e) {
        console.log(e.target)
        e.preventDefault();
    }
}

单击提交按钮时，我的函数search会被调用。但是，如何获取提交的值？

e.target给我整个表单 DOM HTML e.target.value是undefined