How to Access URL Parameters in ReactJS

import React from 'react';

//Parent component - contains main data
class App extends React.Component {
    constructor(props) {
        super(props);
        this.state = { data: [] };
        this.addData = this.addData.bind(this);
    }

    addData(newData){
        let data = this.state.data;
        data.push(newData);
        this.setState({ data });
    }

    render() {
        let data = this.state.data;
        return (
            <div className="col-lg-12 text-center">
            <h1>React Forms - Controlled Component</h1>  
            <AddForm addData={this.addData} data={this.state.data}></AddForm>  
            <hr></hr>
            <ul>
                {data.map( (e,i)=>{
                    return (
                        <li key={i}>
                            {e.user} | {e.game} | {e.points}
                        </li>
                    )
                })

                }
            </ul>            
            </div>
        );
    }
}

// Child component - the Form to add one record
// Controlled Component - source of truth in React
class AddForm extends React.Component{
    constructor(props){
        super(props);
        this.state = { data : {user:'',game:'Galaga',points:0}}
        this.handleChange = this.handleChange.bind(this);
        this.handleSubmit = this.handleSubmit.bind(this);
    }
    
    handleChange(event){
        let {name, value} = event.target;
        let data = this.state.data;
        data[name] = value;
        this.setState({data})
    }
    error=false;
    handleSubmit(event){
        //validate
        event.preventDefault();
        if(!this.error){
            this.props.addData(this.state.data);
            this.setState({ data : {user:'',game:'Galaga',points:0}});
        }
    }

    render(){
        let data = this.state.data;
        return(
            <div className="col-md-8 ml-5">
                <form>
                    <div className="form-row">
                        <div className="col-md-4 mb-3">
                            <label>User:</label>  
                            <input 
                                className="form-control"
                                name="user"
                                value={data.user}
                                onChange={this.handleChange}
                                />  
                        </div>
                        <div className="col-md-4 mb-3">
                            <label>Game:</label>
                            <select 
                                className="form-control"
                                name="game"
                                defaultValue={data.game}
                                onChange={this.handleChange}
                                >
                                <option>Pac-Man</option>
                                <option>Pong</option>
                                <option>Galaga</option>
                                <option>Tetris</option>
                            </select>
                        </div>
                        <div className="col-md-4 mb-3">
                            <label>Points:</label>
                            <input 
                                className="form-control"
                                name="points"
                                type="number"
                                min='0'
                                max='10000'
                                value={data.points}
                                onChange={this.handleChange}
                                /> 
                        </div>
                        <div className="col-md-4 mb-3">
                            <button onClick={this.handleSubmit} className="btn btn-primary">Submit</button>
                        </div>
                    </div>
                </form>
            </div>
        )
    }
}

export default App;