无聊控制input键入内容的增减监听

        
        HTMLElement.prototype.attr = function(k,v){
            if(v){
                return this.setAttribute(k,v);
            }
            return this.getAttribute(k);
        }

        window.clog = function(s,t){
            t = t?'red':'green';
            console.log('%c'+s,'font-size:1.5em;color:'+t);
        }
        
        var inputEvent = function(i,jia,jian){
            i.oninput = function(){
                var len = this.value.length;
                var ilen = this.attr('len')||0;
                if(len<ilen){
                    jian(this.value);
                }else{
                    jia(this.value);
                }
                this.attr('len',len);
            }
        }
        
        window.onload = function(){
            var i = document.getElementById("i");
            inputEvent(i,function(v){
                clog(v,0);
            },function(v){
                clog(v,1);
            });
            
        }