有用的Javascript，长期更新...

1，点击目标区域之外隐藏，运用场景：点击遮罩层，弹层关闭。 

// 点击目标区域之外隐藏
$(document).on("click", function (event) {
	var e = window.event || e;
	obj = $(e.srcElement || e.target);
	if ($(obj).is(selector)) {
		// console.log('内部区域');
		// do something 
	} else {
		// console.log('你的点击不在目标区域');
		// do something  
	}
});

2，JS超出显示省略号

function getStrLen(str, len) {
	if(!str) return;
	var iCount = 0;
	var reg = /[^\x00-\xff]/;
	var result = "";
	for (var i = 0; i < len; i++) {
		if (reg.test(str.charAt(i))) {
			iCount++
		}
		result += str.charAt(i);
		iCount++
	}

	if (result.length < str.length) {
		result += "...";
	}
	return result
}

三、JS日期加月计算；

/** 
 * 日期加月计算 
 * num:要加的月数 
 * sdate:要计算的日期，日期对象 
 */  
function addMonth(num,sdate) {  
    //日期不传默认为当前日期  
    var d = sdate || new Date();  
    //当前月份  
    var oldMonth = d.getMonth();  
    //当前几号  
    var oldDay = d.getDate();  
    //每个月多少天，平年  
    var days = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];  
    //闰年二月为29天  
    var fullYear = d.getFullYear();  
    if ((fullYear % 4 == 0 && fullYear % 100 != 0) || fullYear % 400 == 0) {  
        days[1] = 29;  
    }  
    //加月，设置月为：当前月份+要加的月数  
    d.setMonth(oldMonth + num);  
    //计算月日  
    var newDay = d.getDate();  
    if (oldDay == days[oldMonth]) {  
        if(newDay != oldDay){  
            //设置新日期为：新日期的上个月的最后一天  
            d.setDate(0);  
        }else{  
            //设置为当月最后一天  
            d.setDate(1);  
            d.setMonth(d.getMonth()+1);  
            d.setDate(0);  
        }  
    }  
    //输出年月日，月日不足10前面补0  
    var y = d.getFullYear();  
    var m = d.getMonth() + 1;  
    var dd = d.getDate();  
    if (m < 10) {  
        m = '0' + m;  
    }  
    if (dd < 10) {  
        dd = '0' + dd;  
    }  
    return y + "-" + m + "-" + dd;  
}  
addMonth(2,new Date("2017-02-28"))
// 2017-04-30

四、一个页面应用加个倒计时

var addTimer = function () {
    var list = [],
        interval;

    return function(id, time) {
        if (!interval)
            interval = setInterval(go, 1000);
        list.push({ ele: id, time: time });
    }

    function go() {
        for (var i = 0; i < list.length; i++) {
            document.getElementById(list[i].ele).innerHTML = getTimerString(list[i].time ? list[i].time -= 1 : 0);
            if (!list[i].time)
                list.splice(i--, 1);
        }
    }

    function getTimerString(time) {
        var end = new Date(time);
        var now = new Date();
        var m = Math.round((end - now) / 1000);
        var day = parseInt(m / 24 / 3600);
        var hours = parseInt((m % (3600 * 24)) / 3600);
        var minutes = parseInt((m % 3600) / 60);
        var seconds = m % 60;
        return "还有" + day + "天" + hours + "小时" + minutes + "分" + seconds + "秒";
    }
}();
// 调用
addTimer(id, timestamp);

五、js实现某年某月某天距离如今有多少天,多少分,多少秒,动态显示!

/**
 * @Author   Jone
 * @DateTime 2019-04-04
 * @param    {[type]}   date [js实现某年某月某天距离如今有多少天,多少分,多少秒,动态显示!]
 * @return   {[type]}        [description]
 */
function aa(date) {
    var current = Date();
    var seconds = (Date.parse(current) - Date.parse(date)) / 1000;
    var days = Math.floor(seconds / (3600 * 24));
    seconds = seconds % (3600 * 24);
    var hours = Math.floor(seconds / 3600);
    seconds = seconds % 3600;
    var minutes = Math.floor(seconds / 60);
    seconds = seconds % 60;
    var formatNumber = n => n.toString()[1] ? n.toString() : '0' + n.toString();
    var result = days + '天' + formatNumber(hours) + '小时' + formatNumber(minutes) + '分钟' + formatNumber(seconds) + '秒';
    return result;
}
// 调用
setInterval(() => {
    console.log(aa(time));
}, 1000)