__defineGetter__和__defineSetter__在日期中的应用

日期函数每次取年月日都要调用Date的函数，有点麻烦，通过__defineGetter__可以处理一下，就能通过Date的实例对象直接获取年月日，例如 date.year获取日期对象date的年份。月份因为与正常月份差一个月，可以通过函数自动校正一下，使用起来就更符合习惯了。很多时候我们需要显示一个日期、时间或者日期时间，就可以通过__defineGetter__处理好之后，直接返回对应的数据。

let { log } = console;

Date.prototype.__defineGetter__('year', function() {return this.getFullYear();});
Date.prototype.__defineSetter__('year', function(y) {this.setFullYear(y)});
Date.prototype.__defineGetter__('month', function() {return this.getMonth() + 1;});
Date.prototype.__defineSetter__('month', function(m) {this.setMonth(m-1)});
Date.prototype.__defineGetter__('day', function() {return this.getDate();});
Date.prototype.__defineSetter__('day', function(d) {this.setDate(d)});
Date.prototype.__defineGetter__('hour', function() {return this.getHours();});
Date.prototype.__defineSetter__('hour', function(h) {this.setHours(h)});
Date.prototype.__defineGetter__('minute', function() {return this.getMinutes();});
Date.prototype.__defineSetter__('minute', function(m) {this.setMinutes(m)});
Date.prototype.__defineGetter__('seconds', function() {return this.getSeconds();});
Date.prototype.__defineSetter__('seconds', function(s) {this.setSeconds(s)});

Date.prototype.__defineGetter__("date", function (){return `${this.year}-${(this.month.dbl())}-${this.day.dbl()}`});
Date.prototype.__defineGetter__("time", function (){return `${this.hour.dbl()}:${this.minute.dbl()}:${this.seconds.dbl()}`});
Date.prototype.__defineGetter__("datetime", function (){return `${this.date} ${this.time}`});

// 将数字转换成2位的字符串，不足两位的在前面补0
Number.prototype.dbl = function (){
	return String(this).padStart(2, 0);
}

let num = 2;
log(num.dbl());

function doubleNum(n){
	return String(n).padStart(2, 0);
}

var now = new Date;
log("%O",now); // 这样打印可以看到日期的属性和方法
let { year: y, month: m, day: d } = now;

log("年：%s",y) // 年：2019
log(y, m, d); // 2019 6 20
log(now.date); // 2019-06-20
log(now.time); // 10:56:53
log(now.datetime); // 2019-06-20 10:56:53

　　上面这种写法已经过时了，现在已经不推荐使用__defineGetter__和__defineSetter__。因此可以使用Object.defineProperty来实现，下面是代码

// 将数字转换成2位的字符串，不足两位的在前面补0
Number.prototype.dbl = function (){
	return String(this).padStart(2, 0);
}

Object.defineProperty(Date.prototype, "year", {
	enumerable : true,
  	configurable : true,
	get: function (){
		return this.getFullYear();
	},
	set: function (y){
		this.setFullYear(y);
	}
});

Object.defineProperty(Date.prototype, "month", {
	enumerable : true,
  	configurable : true,
	get: function (){
		return this.getMonth() + 1;
	},
	set: function (m){
		this.setMonth(m - 1);
	}
});

Object.defineProperty(Date.prototype, "day", {
	enumerable : true,
  	configurable : true,
	get: function (){
		return this.getDate();
	},
	set: function (d){
		this.setDate(d);
	}
});

Object.defineProperty(Date.prototype, "hour", {
	enumerable : true,
  	configurable : true,
	get: function (){
		return this.getHours();
	},
	set: function (h){
		this.setHours(h);
	}
});

Object.defineProperty(Date.prototype, "minutes", {
	enumerable : true,
  	configurable : true,
	get: function (){
		return this.getMinutes();
	},
	set: function (m){
		this.setMinutes(m);
	}
});

Object.defineProperty(Date.prototype, "seconds", {
	enumerable : true,
  	configurable : true,
	get: function (){
		return this.getSeconds();
	},
	set: function (s){
		this.setSeconds(s);
	}
});

Object.defineProperty(Date.prototype, "y", {
	get: function (){
		return this.year;
	}
});
Object.defineProperty(Date.prototype, "m", {
	get: function (){
		return this.month;
	}
});
Object.defineProperty(Date.prototype, "d", {
	get: function (){
		return this.day;
	}
});
Object.defineProperty(Date.prototype, "h", {
	get: function (){
		return this.hour;
	}
});
Object.defineProperty(Date.prototype, "min", {
	get: function (){
		return this.minutes;
	}
});
Object.defineProperty(Date.prototype, "s", {
	get: function (){
		return this.seconds;
	}
});

Object.defineProperty(Date.prototype, "date", {
	get: function (){
		// return `${this.y}-${this.m.dbl()}-${this.d.dbl()}`;
		const that = this;
		return function (sep = "-"){
			return `${that.y}${sep}${that.m.dbl()}${sep}${that.d.dbl()}`;
		}
	}
});

Object.defineProperty(Date.prototype, "time", {
	get: function (){
		return `${this.h.dbl()}:${this.min.dbl()}:${this.s.dbl()}`;
	}
});

Object.defineProperty(Date.prototype, "datetime", {
	get: function (){
		// return `${this.date} ${this.time}`;
		const that = this;
		return function (sep = "-"){
			return `${this.date(sep)} ${this.time}`;
		}
	}
});

let d = new Date();
console.log(d.date());
console.log(d.time);
console.log(d.datetime("/"));