js 版 简易计算器, 第一次写,有好的建议虚心接受

var calculator = function(obj){
    this.obj = obj;
    this.maxValue = obj.maxValue;
    this.minValue = obj.minValue;
    this.operationSymbol = obj.operationSymbol;
    this.increasing = obj.increasing;
    this.init(); //Initialization function
};
calculator.prototype = {
    constructor : this,
    init : function(){
        var _this = this;
        if(_this.obj.obj.val() > _this.maxValue || isNaN(_this.obj.obj.val()) != false){
            _this.obj.obj.val(_this.maxValue);
            return;
        }
        switch(_this.operationSymbol){
            case ‘plus‘:
                _this.plus(_this.obj, _this.increasing);
                break;
            case ‘minus‘:
                _this.minus(_this.obj, _this.increasing);
                break;
            case ‘times‘:
                _this.times(_this.obj, _this.increasing);
                break;
            case ‘divide‘:
                _this.divide(_this.obj, _this.increasing);
                break;
            defaults :
                break;
        }
    },
    plus : function(obj,increasing){
        var puls_this = this;
        puls_this.initValue = parseInt(obj.obj.val());
        if(puls_this.initValue >= puls_this.minValue && puls_this.initValue != puls_this.maxValue && isNaN(puls_this.initValue)==false){
            obj.obj.val(parseInt(puls_this.initValue + puls_this.increasing));
        }
    },
    minus : function(obj,increasing){
        var minus_this = this;
        minus_this.initValue = obj.obj.val();
        if(minus_this.initValue != minus_this.minValue && isNaN(minus_this.initValue)==false)
            obj.obj.val(parseInt(minus_this.initValue - minus_this.increasing));
    },
    times : function(obj,increasing){
        var times_this = this;
        times_this.initValue = obj.obj.val();
        if(isNaN(times_this.initValue)==false)
            obj.obj.val(parseInt(times_this.initValue * times_this.increasing));
    },
    divide : function(obj,increasing){
        var divide_this = this;
        divide_this.initValue = obj.obj.val();
        if(isNaN(divide_this.initValue) == false)
            obj.obj.val(parseInt(divide_this.initValue / divide_this.increasing));
    }
};
window.calculator = calculator; 

<a href="javascript:void(0);" onClick="counter(‘defaultValue‘,‘minus‘)">-</a>
<input name="" type="text" value="1" id="defaultValue" />
<a href="javascript:void(0);" onClick="counter(‘defaultValue‘,‘plus‘)">+</a></div>

<script type="text/javascript">
    function counter(obje,symbol){
        new calculator({
            obj:$(‘#‘+obje),
            maxValue : 99,
            minValue : 0,
            operationSymbol : symbol,
            increasing : 1
        });
    }
</script>