You are code should be something like below.
Event handler functions in react can be called with this.functionName but not this.state.functionName. In your case it should be this.clickMonth but not this.state.clickMonth
Now on clicking the button you are rendering Line component. So to render Line component on button click you can set a boolean flag to true and render the Line component accordingly like how I did below
constructor(props){
super(props);
this.state = {
showLine: false,
showLine1: false
}
}
clickMonth = () =>{
this.setState({
showLine: true,
showLine1: false
})
}
clickYear = () =>{
this.setState({
showLine: false,
showLine1: true
})
}
render(){
const { showLine, showLine1 } = this.state;
return(
<div>
{showLine && <Line data={chartjs.monthLine.data} options=
{chartjs.monthLine.options} />}
{showLine1 && <Line data={chartjs.monthLine.data} options=
{chartjs.monthLine.options} />}
<Button color="primary" onClick={this.clickMonth} />
<Button color="primary" onClick={this.clickYear} />
</div>
)
}