webDemo/scope.html at master · dongweizhao/webDemo · GitHub

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<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
</head>
<body>

</body>
<script type="text/javascript">
    function Polygon(sides){
        if (this instanceof Polygon) {
            this.sides = sides;
            this.getArea = function(){
                return 0; };
        } else {
            return new Polygon(sides);
        } }
    function Rectangle(width, height){
        Polygon.call(this, 2);
        this.width = width;
        this.height = height;
        this.getArea = function(){
            return this.width * this.height;
        };
    }
    Rectangle.prototype = new Polygon();
    var rect = new Rectangle(5, 10);
    alert(rect.sides);        //2
</script>
</html>