React: Uncaught type error: this.setState is not a function [duplicate]

I'm new to React, and writing my first web application. I am trying to write a search method that looks through a list of doctors. I get an "Uncaught type error: this.setState is not a function". I tried to add .bind at the end of the function, still got the error. I'm not sure how to proceed. The code is below:

       this.searchBox.addEventListener('keyup', function(text){    
       this.state = {
            doctors: ["Dr Smith", "Dr Jones", "Dr Mary"],
            //list of matched doctors
            matchedDoctors: []
        }
        document.getElementById("demo").innerHTML = "hello world"; 
        var list = [];
        //console.log(this.state.doctors);
        for(var i = 0; i<this.state.doctors.length; i++){
            if(this.state.doctors[i].toLowerCase().includes(text.toString().toLowerCase())){
                list.push(
                    this.state.doctors[i]
                )
            }
        }
        this.setState({matchedDoctors:list});
  }
  );