function input_defaultValue() {                var get_input = document.getElementsByTagName("input");                for(var i = 0; i < get_input.length; i++) {                    if(document.all) {
                        get_input[i].attachEvent('onfocus', function() {                            if(this.value == this.defaultValue) {                                this.value = '';
                            }
                        });
                        get_input[i].attachEvent('onblur', function() {                            if(this.value == '') {                                this.value = this.defaultValue;
                            }
                        });
                    } else {
                        get_input[i].addEventListener('focus', function() {                            if(this.value == this.defaultValue) {                                this.value = '';
                            }
                        });
                        get_input[i].addEventListener('blur', function() {                            if(this.value == '') {                                this.value = this.defaultValue;
                            }
                        });
                    };
                }
            };
            input_defaultValue();

就改成了if（）{}就對了，也沒細看。
改進的話當然是能力檢測了

            if(document.addEventListener) {                //
            } else if(document.attachEvent()) {                //
            } else {

            }