JSFiddle - React, Tailwind, and code Playground

JavaScript

var cats=['Abyssinian', 'Balinese', 'Bombay', 'Birman'];

Array.prototype.contains=function(incattype){
document.write("hhhh");        
    for(var i=0; i<cats.length;i++){
            
        if(cats[i]==incattype) {
            return true;
        } else{
             return false;
        }      
    }
};
    

  var catslist=['Abyssinian', 'Balinese', 'Bombay11' ];
        
    for(var i=0; i<catslist.length;i++){
       
        document.write(cats.contains[catslist[i]]);
    }        
        
       
document.write(typeof Array.prototype.contains);