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I'm developing a webpage displaying the scheduled pipelines from all projects of a GitLab instance. The scheduled time is expressed using CRON expressions, i.e. five digits as follows:

Because not all future users of my webpage are familiar with CRON expressions, I wrote a script for translating it into a human-readable time expression.

Some important information for understanding the logic behind the code:

• 
  "7" is not used as an alias for "Sunday" on my GitLab instance.


• 
  Timezones are not taken into account (...yet). I'm considering all CRON expressions as UTC times for now.


• Times are expressed in the 24 hours format (so 11:23PM is 23h23)


• The pipelines that we launch take a lot of time to be fully executed, which is why we don't allow the first digit of the CRON expression to be *.

Some examples of cron-to-string conversion:

0 4 * * * * → "Runs at 04h00 every day"

0 23 * * 0 → "Runs at 23h00 on Sundays"

0 4 1 * * → "Runs at 04h00 on the 1st day of every month"

The code

function convertCronToString(cronExpression) 
 var cron = cronExpression.split(" ");
 var minutes = cron[0];
 var hours = cron[1];
 var dayOfMonth = cron[2];
 var month = cron[3];
 var dayOfWeek = cron[4];

 var cronToString = "Runs at ";

 // Formatting time if composed of zeros
 if (minutes === "0") minutes = "00";
 if (hours === "0") hours = "00";
 // If it's not past noon add a zero before the hour to make it look like "04h00" instead of "4h00"
 else if (hours.length === 1 && hours !== "*") 
 hours = "0" + hours;
 
 // Our activities do not allow launching pipelines every minute. It won't be processed.
 if (minutes === "*") 
 cronToString =
 "Unreadable cron format. Cron will be displayed in its raw form: " +
 cronExpression;
 

 cronToString = cronToString + hours + "h" + minutes + " ";

 if (dayOfWeek === "0,6") dayOfWeek = "on weekends";
 else if (dayOfWeek === "1-5") dayOfWeek = "on weekdays";
 else if (dayOfWeek.length === 1) 
 if (dayOfWeek === "*" && dayOfMonth === "*") dayOfWeek = "every day ";
 else if (dayOfWeek === "*" && dayOfMonth !== "*") 
 cronToString = cronToString + "on the " + dayOfMonth;
 if (
 dayOfMonth === "1" else if (dayOfWeek !== "*" && dayOfMonth === "*") 
 switch (parseInt(dayOfWeek)) 
 case 0:
 dayOfWeek = "on Sundays";
 break;
 case 1:
 dayOfWeek = "on Mondays";
 break;
 case 2:
 dayOfWeek = "on Tuesdays";
 break;
 case 3:
 dayOfWeek = "on Wednesdays";
 break;
 case 4:
 dayOfWeek = "on Thursdays";
 break;
 case 5:
 dayOfWeek = "on Fridays";
 break;
 case 6:
 dayOfWeek = "on Saturdays";
 break;
 default:
 cronToString =
 "Unreadable cron format. Cron will be displayed in its raw form: " +
 cronExpression;
 return cronToString;
 
 
 cronToString = cronToString + dayOfWeek + " ";
 

 return cronToString;

Question

How could this code be optimized?

Additional information

• This method is part of a Vue.JS component so I apologize if I forgot to translate some of the Vue-specific into Vanilla Javascript.


• I have not implemented the code in case the pipeline is supposed to run on a given number of days of the week/month when provided as a suite of numbers separated by commas.

You do a lot of tests. It would be simplier if you implement a few objects containing your different values and you just display these values.

You'd have to do enough objects to cover all cases but you limit the tests to the minimum this way.

Example :

// I won't print every cases but you got the idea
let dayOfWeekWhenNoMonthIsSpecified = 
 '*' : 'every day', '0' : 'on Sundays', '1' : 'on Mondays',
 '0,6' : 'on weekends', '1-5' : 'on weekdays'
;

cronToString = "Runs " + dayOfWeekWhenNoMonthIsSpecified[cron[4]];