React and typescript using datepicker error cant find module

I was using React and Typescript. I installed react-datepicker and imported into my code. This error occurred:

module can't find react-datepicker

But I have react-datepicker module in node_module. why does the error occure?

I'm using TSX file method.

todo.component.tsx

import * as React from 'react'; 
import * as classNames from 'classnames';
import TodoList from './todo.list';
import { Todo } from './../todo.interface';
import { Button } from 'react-bootstrap';
import DatePicker from 'react-datepicker';
import moment from 'moment';
import 'react-datepicker/dist/react-datepicker.css';
const KEYCODE_ENTER = 13;
export default class TodoComponent extends React.Component
<TodoComponentProps, TodoComponentState> {
constructor(props) {
super(props);
    this.state = {
        description: '',
        valid: true,
        items: [], text: '',
        startDate: '',
    };
this.removeTodos = this.removeTodos.bind(this);
    this.handleChange = this.handleChange.bind(this);
}
handleChange(date) {
    this.setState({
        startDate: date
    });
}
addTodos(e) {
    e.preventDefault();
    this.setState({
        items: [this.state.text, ...this.state.items],
        text: ''
    });
}
removeTodos(name, i) {
    let items = this.state.items.slice();
    items.splice(i, 1);
    this.setState({
        items
    });
}

updateValue(e) {
    this.setState({ text: e.target.value })
}

openNav() {
    document.getElementById("mySidenav").style.width = "250px";
    console.log(this)
}

closeNav() {
    document.getElementById("mySidenav").style.width = "0";
}

setDescription(event) {
    this.setState({ valid: true, description: event.target.value });
}
addTodo(event) {
    if (event && event.keyCode !== KEYCODE_ENTER && event.type !== 'click') {
        return;
    }
    if (!this.state.description.length || this.state.description.length > 50) {
        this.setState({ valid: false });
    } else {
        this.props.addTodo(this.state.description);
        this.setState({ description: '' });
    }
}

render() {
    let inputClass = classNames('form-group', {
        'has-error': !this.state.valid
    });

return (
        <div>
            <div className="container" onKeyDown={this.addTodo.bind(this)}>
                <div className="row">
                    <div className="col-sm-12">
                        <h2 className="text-center">What do you need to do?</h2>
                        <br />
                        <br />
                    </div>
                    <div className="col-sm-6 col-sm-offset-3">
                        <div className={inputClass}>
                            <label className="control-label">Task description</label>
                            <input className="form-control input-lg" type="text" value={this.state.description} onChange={this.setDescription.bind(this)} />
                        </div>
                    </div>
                    <div className="col-sm-3 col-sm-offset-3">
                        <button className="btn btn-success btn-block" onClick={this.addTodo.bind(this)}>
                            <i className="fa fa-plus"></i> Add Todo
                    </button>
                    </div>
                    <div className="col-sm-3">
                        <button className="btn btn-danger btn-block" onClick={this.props.removeDoneTodos.bind(this)}>
                            <i className="fa fa-trash-o"></i> Remove done todos
                    </button>
                    </div>
                </div>
<br />
                <br />

                <div className="row">
                    <div className="col-sm-6 col-sm-offset-3" onClick={this.openNav.bind(this)}>
                        <TodoList {...this.props} />
                    </div>
                </div>
                <div id="mySidenav" className="row offcanvas">
                    <div className="sideNav">
                        <span onClick={this.closeNav.bind(this)}><i className="fa fa-lg fa-close"></i></span>
                        <br /><br />
<div className="due">
                            <DatePicker
                                inline
                                selected={this.state.startDate}
                                onChange={this.handleChange}
                            />
                        </div>
                        <hr />
                        <div className="remind">
                        </div>
                        <hr />
                        <div className="sublist" >
                            <TodosubList items={this.state.items} removeTodos={this.removeTodos} />
                            <form onSubmit={(e) => this.addTodos(e)}>
                                <input
                                    placeholder="Add SubTask"
                                    value={this.state.text}
                                    onChange={(e) => { this.updateValue(e) }}
                                />
                                <button type="submit">+</button>
                            </form>
                        </div>
                        <hr />
                        <div className="description">
                        </div>
                        <hr />
                        <div className="comment">
                        </div>
                        <hr />
                        <div className="commentIn">
                        </div>
</div>
                </div>
            </div>
        </div>
    );
}
}



class TodosubList extends React.Component<{ items?: any; removeTodos: any; }, {}> {
removeItem(item, i) {
    this.props.removeTodos(item, i);
}
render() {
    return (
        <ul className="sub">
            {this.props.items.map((todo, i) => {
                return <li onClick={() => { this.removeItem(todo, i) }} key={i}>{todo}</li>
            })}
        </ul>
    );
}
}


interface TodoComponentProps {
todos: Todo[];
addTodo(description: string): void;
addTodos?: any;
toggleTodo: React.MouseEventHandler;
editTodo: React.MouseEventHandler;
removeTodo: React.MouseEventHandler;
removeDoneTodos: React.MouseEventHandler;
}

interface TodoComponentState {
description?: string;
subdescription?: any;
valid?: boolean;
items?: any;
text?: any;
startDate?: any;
}  

cmd error:

error:cant find module react-datepicker.