syntax error using arrow function in react

Question

My handleClick arrow function got unexpected error I have no clue why, couldn't spot any error.

class HelloWidget extends React.Component {
    constructor(props) {
      super(props);
      this.names_holder = [];
      this.state = {
        name: []
      };
    }

    handleClick = () => { //error here
      let random = this.names_holder.concat(Math.ceil(Math.random() * 10) + 3);
      this.setState({
        name: random
      });
    }

    render() {
      return <div className = "widget" >
        < button onClick = {
          this.handleClick
        } > Random concat < /button> {
          JSON.stringify(this.state.name)
        } < /div>;
    }
}

https://jsfiddle.net/zLkbfdnm/