Javascript自定义日期格式化

Date MDN

参考java类java.text.SimpleDateFormat

function DateFormat(date, pattern) {
    if(arguments.length == 1 && typeof date == 'string'){
        pattern = date;
        date = null
    }
    var _p = pattern || 'yyyy/MM/dd HH:mm:ss'
    date = date||new Date()

    var _PLACEGOLDER = '_@@_'

    var AP = ['AM', 'PM']
    var WEEKDAY = ['日','一','二','三','四','五','六', '礼拜']

    var textIgnore = []
    var _i = 0

    _p = _p.replace(/('.*')/g, function(match){
        textIgnore.push(match.substring(1, match.length-1) )
        return _PLACEGOLDER
    })

    var lengthHandler= function(str, length){
        str += ''
        var l = length - str.length
        if(l > 0) {
            return (Math.pow(10, l)+'').substr(1) + str
        }else {
            return str.substr(0-l, length)
        }
    }

    var patterns = {}
    //Year
    patterns['y+'] = function (match, offset, string){
        let target = date.getFullYear()
        return lengthHandler(target, match.length)
    }
    //Month in year
    patterns['M+'] = function (match, offset, string){
        let target = date.getMonth() + 1
        return lengthHandler(target, match.length)
    }
    //Day in month
    patterns['d+'] = function (match, offset, string){
        let target = date.getDate()
        return lengthHandler(target, match.length)
    }
    //Am/pm marker
    patterns['a'] = function (match, offset, string){
        let target = date.getHours()
        if(target >= 0 && target < 12){
            target = AP[0]
        }else{
            target = AP[1]
        }
        return target
    }

    //Hour in day (0-23)
    patterns['H+'] = function (match, offset, string){
        let target = date.getHours()
        return lengthHandler(target, match.length)
    }

    //Hour in am/pm (1-12)
    patterns['h+'] = function (match, offset, string){
        let target = date.getHours()
        target = Math.abs(target - 12)
        return lengthHandler(target, match.length)
    }

    //Minute in hour(0-59)
    patterns['m+'] = function (match, offset, string){
        let target = date.getMinutes()
        return lengthHandler(target, match.length)
    }

    //Seconds in minute (0-59)
    patterns['s+'] = function (match, offset, string){
        let target = date.getSeconds()
        return lengthHandler(target, match.length)
    }

    //Millisecond
    patterns['S+'] = function (match, offset, string){
        let target = date.getSeconds()
        return lengthHandler(target, match.length)
    }

     //Day name in week
     patterns['E+'] = function (match, offset, string){
        let target = date.getDay()
        let length = match.length
        if(length == 1){
            return WEEKDAY[target]
        }else if(length == 2){
            return (WEEKDAY[7]||'周') + WEEKDAY[target]
        }
        
    }

    //Time zone
    patterns['z+'] = function (match, offset, string){
        let target = date.getTimezoneOffset()
        if(target > 0){
            return '-' + (target/60)
        }
        return '+' + (-target/60)
    }

    for(var k in patterns) {
        _p = _p.replace(new RegExp(k, 'g'), patterns[k]);
    }

    _p = _p.replace(new RegExp(_PLACEGOLDER, 'g'), function(){
        return textIgnore[_i++]
    })

    return _p
}

var str = DateFormat(new Date(), "[ '北京时间' z yyyy-MM-dd a hh:mm:ss.SSSS EE]")
console.log(str)
console.log(DateFormat("[ '北京时间' z yyyy-MM-dd a hh:mm:ss.SSSS EE]"))
console.log(DateFormat())
//[ 北京时间 +8 2018-09-10 PM 06:59:31.0031 礼拜一]
//[ 北京时间 +8 2018-09-10 PM 06:59:31.0031 礼拜一]
//2018/09/10 18:59:31