strftime.js

strftime.js

// ES6 strftime(3) function that supports FDxcAaBbCdemuwYynt% for en_US only
// (only for dates, not datetimes)
Date.prototype.format = function(f) {
	const t=this,p=(v,f)=>v.toString().length==1?f+v:v,Y=t.getFullYear(),mo=t.getMonth()+1,dm=t.getDate(),u=t.getDay(),A=['Sunday','Monday','Tuesday','Wednesday','Thursday','Friday','Saturday'][u%7],B=['January','February','March','April','May','June','July','August','September','October','November','December'][mo-1]
	return ['%Y-%m-%d','%m/%d/%y','%m/%d/%Y','%a %b %e %Y',A,A.slice(0,3),B,B.slice(0,3),Y/100|0,p(dm,'0'),p(dm,' '),p(mo,'0'),u,u%7,Y,Y%100,'\n','\t','%'].reduce((_, s, i)=>_.replace(new RegExp('%'+'FDxcAaBbCdemuwYynt%'[i],'g'),s),f)
}

// Unit tests
!() => {
var date = new Date('2016-04-02'), assert = require('assert')
assert.equal(date.format('%F _ %Y _ %D _ %x'), '2016-04-02 _ 2016 _ 04/02/16 _ 04/02/2016')
assert.equal(date.format('%A _ %a _ %B _ %b'), 'Saturday _ Sat _ April _ Apr')
assert.equal(date.format('%C _ %c _ %\d _ %e'), '20 _ Sat Apr  2 2016 _ 02 _  2')
assert.equal(date.format('%m _ %u _ %w _ %Y'), '04 _ 6 _ 6 _ 2016')
assert.equal(date.format('%y _ %n _ %t _ %%'), '16 _ \n _ \t _ %')
}