Date format exception in reactjs

i want to send an api request to some url with that i want to send two query params(start and end date). i used to two input tag for the dates and passed it to url but the "date format exception" is shown

//search page
state= {
    startDate: null,
    endDate: null
    };

    startDatePicker= event=>{
        event.preventDefault();
        var date= event.target.value;
      this.setState({
        startDate: date
      });
    }
     endDatePicker= (event)=>{
      event.preventDefault();
      let date= event.target.value;
      this.setState({
        endDate: date
      });
    }
    submitHandler= (event) =>{
        event.preventDefault();
        this.props.onSearchByDate(this.state.startDate, this.state.endDate);
    }
    render() {
        console.log(this.state.endDate);
        return (
            <div>
                <input type= "date" placeholder= "yyyy-mm-dd"
                 onChange= {this.startDatePicker} name= "startDate"/><br/>
                <input type= "date" 
                    onChange= {this.endDatePicker} name= "endDate"/>
                <button onClick= {this.submitHandler}>
                    Search</button>
            </div>
        );
    }
}
// api page
export const fetchByDate= (startDate, endDate) => dispatch =>{
    console.log(startDate);
    fetch("https://api.nasa.gov/neo/rest/v1/feed?start_date=startDate&end_date=endDate&api_key=[demokey]")
    .then(res => res.json())
    .then(data =>{
        console.log(data);
        return dispatch({
            type: actions.fetchByDates, data: data
        });
    });
}