cron-js-parser

Library that provides two methods which help in UI and Backend based parsing of cron expression. Following methods are found to be most common use cases, also culprits for bloating the code :

1. parseHumanReadable:

   Outputs a human readable description of the cron schedule from a cron expression or cron values. For example, given the expression "*/5 * * * *" it will output "Every 5 minutes".

   Example :

   let language = 'en' //english
   let obj = {
     atSeconds: [1, 5, 10],
     runEveryXMins: {
         startAt: 10,
         every: 10
     },
     runEveryHourInRange: {
         from: 2,
         to: 20
     },
     isEveryDay: true,
     atYears: [2020, 2022]
   };
   console.log(parseHumanReadable("",obj,lang))
   lang = 'fr' //French
   console.log(parseHumanReadable("1,5,10 10/10 2-20 * 1 ? 2020,2022",{},lang))
   
   Output : 
   At 1, 5, and 10 seconds past the minute, every 10 minutes, starting at 10 minutes past the hour, between 02:00 AM and 08:59 PM, every day, only in January, only in 2020 and 2022
   
   1, 5, et 10 secondes après la minute, toutes les 10 minutes, départ 10 minutes après l'heure, de 02:00 AM à 08:59 PM, tous les jours, uniquement en janvier, uniquement en 2020 et 2022

2. parseCronExpression: Outputs a cron expression from a set of values (Look below for Options section to understand all the possible values).

   Example :

   let obj = {
     atSeconds: [1, 5, 10],
     runEveryXMins: {
       startAt: 1,
       every: 10
     },
     runEveryHourInRange: {
       from: 2,
       to: 20
     },
     runOnWeekDay: {
       isLastWeek: false,
       dayIndex: 6,
       weekIndex: 3
     },
     isEveryDay: true,
     atYears: [2020, 2022]
   };
   console.log(parseCronExpression(obj))
   
   Output : 
   1,5,10 1/10 2-20 * * 6#3 

Note : Deparser will be added in future.

Support

• Quartz Scheduler
• Javascript
• Typescript
• Nodejs
• Browser

Options (keys and expected values' type)

isEverySecond?: boolean
isEveryMinute?: boolean
isEveryHour?: boolean
isEveryDay?: boolean
isEveryMonth?: boolean
isEveryYear?: boolean
atSeconds?: []
atMins?: []
atHours?: []
atDays?: []
atMonths?: [],
atWeekDays?:[],
atYears?: [],
runEveryXSeconds?: {
  startAt: number,
  every: number
},
runEveryXMins?: {
  startAt: number,
  every: number
},
runEveryXHours?: {
  startAt: number,
  every: number
},
runEveryXDays?: {
  startAt: number,
  every: number
},
runEveryXMonths?: {
  startAt: number,
  every: number
},
runEveryXWeekDays?: {
  startAt: number,
  every: number
},
runEveryXYears?: {
  startAt: number,
  every: number
},
runEverySecondInRange: {
  from: number,
  to: number
},
runEveryMinuteInRange: {
  from: number,
  to: number
},
runEveryHourInRange: {
  from: number,
  to: number
},
runEveryDayInRange: {
  from: number,
  to: number
},
runEveryMonthInRange: {
  from: number,
  to: number
},
runEveryWeekInRange: {
  from: string,
  to: string
},
runEveryYearInRange: {
  from: number,
  to: number
},
runOnWeekDay:{
  dayIndex:number,
  weekIndex?:number,
  isLastWeek:boolean
}

----atWeekDays implies every week----

Things to keep in mind

• Values that need to be set are different for runEveryXWeekDays && runEveryWeekInRange (See section below Values to understand)

runEveryXWeekDays = {
  startAt:1,
  every:2
} // => start on Sunday and every 2 days

runEveryWeekInRange = {
  from:'MON',
  to:'THU'
} // => start from Monday till Thursday

runOnWeekDay:{
  dayIndex:2,
  isLastWeek:true
} // => on Last Tuesday

runOnWeekDay:{
  dayIndex: 3,
  isLastWeek:false,
  weekIndex: 2
} // => on Second Wednesday

runOnWeekDay:{
  dayIndex:2,
  isLastWeek:true,
  weekIndex: 7 // value will not be considered as 'isLastWeek=true'
} // => on Last Tuesday

Values to understand

• 1 - SUN - Sunday
• 2 - MON - Monday
• 3 - TUE - Tuesday
• 4 - WED - Wednesday
• 5 - THU - Thursday
• 6 - FRI - Friday
• 7 - SAT - Saturday

Important Links to refer for Quartz Scheduler

• https://github.com/bradymholt/cronstrue - Dependency package
• http://www.quartz-scheduler.org/documentation/quartz-2.3.0/tutorials/crontrigger.html
• https://www.freeformatter.com/cron-expression-generator-quartz.html