jQuery.fn.maxLength = function(max){    this.each(function(){        var type = this.tagName.toLowerCase();        var inputType = this.type? this.type.toLowerCase() : null;        if(type == "input" && inputType == "text" || inputType == "password"){            //Apply the standard maxLength            this.maxLength = max;        }        else if(type == "textarea"){            this.onkeypress = function(e){                var ob = e || event;                var keyCode = ob.keyCode;                var hasSelection = document.selection? document.selection.createRange().text.length > 0 : this.selectionStart != this.selectionEnd;                return !(this.value.length >= max && (keyCode > 50 || keyCode == 32 || keyCode == 0 || keyCode == 13) && !ob.ctrlKey && !ob.altKey && !hasSelection);            };            this.onkeyup = function(){                if(this.value.length > max){                    this.value = this.value.substring(0,max);                }            };        }    });};//用法$('#mytextarea').maxLength(500);