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);                            }                        };                    }                });            };  

    $('#phone').maxLength(4);