ECMAScript6 中 类的封装与继承

<script type="text/javascript">
    class OFunction{
        constructor(args){
        }
        setValue(val){
            if(val !== undefined && val != null){
                return val;
            }else{
                return ‘‘;
            }
        }
    }
    class Box extends OFunction{
        constructor(args){
            super(args);
            this.width = super.setValue(args.width) !== ‘‘ ? this.args.width : ‘120‘; 
            this.height = super.setValue(args.height) !== ‘‘ ? this.args.height : ‘60‘;
        }
    }
    class Popup extends Box{
        constructor(args){
            super(args);
            this.args = super.setValue(args) !==‘‘ ? args : {} ;
            this.position = super.setValue(args.position) !== ‘‘ ? this.args.position : ‘center‘;  //the position of this popup;
            this.backgroundColor = super.setValue(args.bg) !== ‘‘ ? this.args.bg : ‘rgba(0,0,0,.6)‘;  //the background-color of this popup;
        }
        getPosition(){
            return this.position;
        }
        getBackgroundColor(){
            return this.backgroundColor + this.more();
        }    
    }
        
    var args={‘position‘:‘left‘,‘bg‘:‘red‘};
    var p=new Popup(args);
    console.log(p.getBackgroundColor())
</script>