jquery限制文本框输入字符长度详解编程语言

    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);   
                        }   
                    };   
                }   
            });   
        };  

使用方法：

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