JavaScript 全形數字轉半形數字

function isValue(val){
    var v = val.value;
    if(v == 'NaN' || v == null || v == ''){
        return 0;
    }else{
        //全行轉半型
        result="";
        for(i=0;i < v.length;i++){        
         if( v.charCodeAt(i)== 12288){
                result+=" ";
         }else{
                if(v.charCodeAt(i) > 65280 && v.charCodeAt(i) < 65375){
                 result += String.fromCharCode(v.charCodeAt(i) - 65248);
                }else{
                 result += String.fromCharCode(v.charCodeAt(i));
                }
         }
        }
        val.value = result;
        v=result;
        return v;
    }
}