How to call prototype functions correctly in javascript?

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Javascript

inheritance

I have the following code with an object called Map defined in a namespace RHCA. Map's prototype is assigned an object containing the following methods.

RHCA.Map = function(centerCoords){
    this.geojson = null;
    this.map = null;
    this.initZoom = 0;
    this.mapColors = [];
    this.mapCenter = centerCoords.slice(0);
    this.geoJsonProperty = null;
    this.dataFieldsMap;
};

RHCA.Map.prototype = {
	setColorRange :function(population){
    	        console.log(this);
		
		var color; // set color according to population value
		... 		

		return  color
	},

	setStyle : function(feature){
    	    console.log(this);
    	    var population =  feature.properties.pop10;
    
    	    var countyColor = this.setColorRange(population);
    	    return {
        	fillColor: countyColor,
        	weight: 0.5,
        	opacity: 1,
        	color: '#4e4e4e',
        	fillOpacity: 0.9,
        	fillRule: 'evenodd',
        	className:'svg-custom'
    	    };
	},

	
	render : function (){
    	     console.log(this);
    	     var self  = this;
    	     var southWest = L.latLng(20.0, -114.0);
    	     var northEast = L.latLng(40.0,-88.0);
    	     var boundRect = L.latLngBounds(southWest, northEast);
    
    	     self.initZoom = self.setZoomLevel();
    
    	     // map object with options
    	     self.map = L.map('map',{
        	center: self.mapCenter,
        	zoom: self.initZoom,
        	maxZoom: self.initZoom+2,
        	minZoom: self.initZoom-0.25,
        	// maxBounds: boundRect,
        	zoomControl:true,
        	reUseTiles:true,
        	unloadInvisibleTiles:true
    	    });
    
    	   // create geojson layer and add it to map   
    	   self.geojson = L.geoJson(countyBoundaries,{
        	style: self.setStyle,
        	onEachFeature: self.onEachFeature
    	   });
    
    	   self.geojson.addTo(self.map);
	}
};

Then i create the Map object like this.

var map = new RHCA.Map([-31,99]);

I then call the render() function on the map object which will then call setStyle(). setStyle() then calls setColor().

I got the following error from the browser when i called setColorRange() in setStyle() function.

Uncaught TypeError: this.setColorRange is not a function.

When i print 'this' using console.log() in render() it points to the RHCA.Map object,
but when i print 'this' in the setStyle() function it points to the Window Object. I need 'this' to point to the RHCA.Map object instead.

All help is appreciated. Thanks you.

What I have tried:

I tried changing this.setColorRange in the setStyle() function to RHCA.Map.setColorRange but it produces the same error as before.