JSFiddle - React, Tailwind, and code Playground

JavaScript

function Map(sizeX, sizeY)
{
    this.sizeX = sizeX;
    this.sizeY = sizeY;
    // you're not using these arrays. Why are they in your example code?
    var cityArr = [],
        cityXY = [];  
}
Map.prototype = {
    generateCity: function(cityNum) { 
        console.log("cityNum: " + cityNum);
    }
}

var $ = new Map(10,10);
$.generateCity(2);