Migrating from D3.js v3 to D3.js v4 not working - a select issue?

d3.select('#rectangle').on('click', function(){ new Rectangle(); });

var w = 600, h = 500;
var svg = d3.select('body').append('svg').attr("width", w).attr("height", h);

function Rectangle() {
    var self = this, rect, rectData = [], isDown = false, m1, m2, isDrag = false;
    
    svg.on('mousedown', function() {
    		console.log(isDown);
        m1 = d3.mouse(this);
        if (!isDown && !isDrag) {
            self.rectData = [ { x: m1[0], y: m1[1] }, { x: m1[0], y: m1[1] } ];
            self.rectangleElement = d3.select('svg').append('rect').attr('class', 'rectangle').call(dragR);
            self.pointElement1 = d3.select('svg').append('circle').attr('class', 'pointC').call(dragC1);
            self.pointElement2 = d3.select('svg').append('circle').attr('class', 'pointC').call(dragC2);            
            self.pointElement3 = svg.append('circle').attr('class', 'pointC').call(dragC3);
            self.pointElement4 = svg.append('circle').attr('class', 'pointC').call(dragC4);
            updateRect();
            isDrag = false;
        } else { 
            isDrag = true;
        }
        isDown = !isDown;   
    })
    
    .on('mousemove', function() {
        m2 = d3.mouse(this);
        if(isDown && !isDrag) { 
            self.rectData[1] = { x: m2[0] - 5, y: m2[1] - 5};
            updateRect();
        } 
    });  
    
    function updateRect() {  
        self.rectangleElement
        		.attr("x", self.rectData[1].x - self.rectData[0].x > 0 ? self.rectData[0].x : self.rectData[1].x)
            .attr("y", self.rectData[1].y - self.rectData[0].y > 0 ? self.rectData[0].y :  self.rectData[1].y)
            .attr("width", Math.abs(self.rectData[1].x - self.rectData[0].x))
            .attr("height", Math.abs(self.rectData[1].y - self.rectData[0].y));  

        var point1 = self.pointElement1.data(self.rectData);
        point1.attr('r', 5)
              .attr('cx', self.rectData[0].x)
              .attr('cy', self.rectData[0].y);        
        var point2 = self.pointElement2.data(self.rectData);
        point2.attr('r', 5)
              .attr('cx', self.rectData[1].x)
              .attr('cy', self.rectData[1].y);
        var point3 = self.pointElement3.data(self.rectData);
        point3.attr('r', 5)
              .attr('cx', self.rectData[1].x)
              .attr('cy', self.rectData[0].y);        
        var point3 = self.pointElement4.data(self.rectData);
        point3.attr('r', 5)
              .attr('cx', self.rectData[0].x)
              .attr('cy', self.rectData[1].y);
    }
    
    var dragR = d3.drag().on('drag', dragRect);
    
    function dragRect() {
        var e = d3.event;
        for(var i = 0; i < self.rectData.length; i++){
            self.rectangleElement
                .attr('x', self.rectData[i].x += e.dx )
                .attr('y', self.rectData[i].y += e.dy );
        }
        self.rectangleElement.style('cursor', 'move');
        updateRect();
    }
    
    var dragC1 = d3.drag().on('drag', dragPoint1);
    var dragC2 = d3.drag().on('drag', dragPoint2);
    var dragC3 = d3.drag().on('drag', dragPoint3);
    var dragC4 = d3.drag().on('drag', dragPoint4);
    
    function dragPoint1() {
        var e = d3.event;
        self.pointElement1
            .attr('cx', function(d) { return d.x += e.dx })
            .attr('cy', function(d) { return d.y += e.dy });        
        updateRect();   
    }   
    
    function dragPoint2() {
        var e = d3.event;
        self.pointElement2
            .attr('cx', self.rectData[1].x += e.dx )
            .attr('cy', self.rectData[1].y += e.dy );
        updateRect();   
    }   
    
    function dragPoint3() {
        var e = d3.event;
        self.pointElement3
            .attr('cx', self.rectData[1].x += e.dx )
            .attr('cy', self.rectData[0].y += e.dy );     
        updateRect();   
    }   
    
    function dragPoint4() {
        var e = d3.event;
        self.pointElement4
            .attr('cx', self.rectData[0].x += e.dx )
            .attr('cy', self.rectData[1].y += e.dy );
        updateRect();   
    }   
    
}//end Rectangle

svg {
    border: solid 1px red;
}

rect {
    fill: lightblue;
    stroke: blue;
    stroke-width: 2px;
}

<button id='rectangle'>Rectangle</button>
<script src="https://d3js.org/d3.v4.js" charset="utf-8"></script>