Chartjs-Not able to pass array of data to chart.js in React

Instead of componentWillMount you can add posts in componentDidMount.

import ReactDOM from "react-dom";
import Axios from 'axios';
import {Bar} from 'react-chartjs-2';
class Chart extends React.Component{
  constructor(props){
    super(props);
    this.state = {
      chartData:props.chartData || {}
    }
  }

  static defaultProps = {
    displayTitle:true,
    displayLegend: true,
    legendPosition:'right',
    location:'City'
  }

  render(){
    return (
      <div className="chart">
        <Bar
          data={this.state.chartData}
          options={{
            title:{
              display:this.props.displayTitle,
              text:'State-Wise Bar Chart',
              fontSize:25
            },
            legend:{
              display:this.props.displayLegend,
              position:this.props.legendPosition
            }
          }}
        />
        </div>
    )
  }
}

class CaseList extends React.Component {
    constructor(props) {
        super(props)

        this.state = {
             posts: [] ,
             chartData:{}
        }
    }

getchartData(states,num){
  console.log("states",states,"num",num)
this.setState({
        chartData:{
          labels: states,
        datasets: [
          {
            label:'No. of Positive Cases',
            data:num,
            backgroundColor:[

              'rgba(255,3,0,1)',
              'rgba(219,3,0,1)',
              'rgba(152,3,0,1)',
              'rgba(255,3,0,0.7)',
              'rgba(101,191,217,1)',
              'rgba(101,191,217,0.59)',
              'rgba(101,79,161,0.98)',
              'rgba(208,79,197,0.98)',
              'rgba(208,79,197,0.65)',
              'rgba(43,144,197,1)',
              ]
          }
        ]
      }
      },()=>{console.log(this.state.chartData)})
    }

componentDidMount() {
        Axios.get('https://api.covid19india.org/data.json')
        .then(response => {
            this.setState({posts:response.data.statewise});
            const posts = response.data.statewise
            var states=[]
            var num=[]

            for (var i=1;i<posts.length;i+=1) {
              states[i-1]=posts[i].state
              num[i-1]=posts[i].confirmed
          }
          this.getchartData(states,num);
            })
        .catch(error => {
            console.log(error)
        })
    }

render(){
return(
<div>
{Object.keys(this.state.chartData).length>0 &&<Chart chartData={this.state.chartData} />}
</div>
  )
}
}
const rootElement = document.getElementById("root");
ReactDOM.render(
    <CaseList />,
  rootElement
);