Javascript - Subtract fields time

What are some sample values and the results using your script?

If one uses values like "9:00 am" for the start and "12:30 pm" for the end time I get "NaN" or "Not a Number".

In order to perform simple arithmetic calculations one needs to use numeric values. These values are formatted like sign (+/-) followed by 1 more numbers in the range of 0-9, a decimal point and then more numeric digits. The ":" and "am" or "pm" are not numerics. Including any of those values will change the type of value from "number" to "string". There is no "-" operator for strings The "+" operator when used with a strings concatenates the values and does not add the values.

With some advanced programing using the RegExp object one can tease out the hours and minutes. With the hours and minutes one has a couple of options for computing the elapsed times.  This approach will work for times within the same day but fails if the times occur on different dates. In this case one needs to adjust for difference in the dates since each day represents a 24 hour difference that needs to be included. This is further complicated by having to deal with the time changes for DST, Day Light Savings Time, or Summer Time. This will add one hour in the fall sue the turn back of the clocks at 2:00 am.

Timesheets that use start and end times perform your calculation 7 times a week. Have you searched for "Timesheets"?

2What are some sample values and the results using your script?

If one uses values like "9:00 am" for the start and "12:30 pm" for the end time I get "NaN" or "Not a Number".

In order to perform simple arithmetic calculations one needs to use numeric values. These values are formatted like sign (+/-) followed by 1 more numbers in the range of 0-9, a decimal point and then more numeric digits. The ":" and "am" or "pm" are not numerics. Including any of those values will change the type of value from "number" to "string". There is no "-" operator for strings The "+" operator when used with a strings concatenates the values and does not add the values.

With some advanced programing using the RegExp object one can tease out the hours and minutes. With the hours and minutes one has a couple of options for computing the elapsed times.  This approach will work for times within the same day but fails if the times occur on different dates. In this case one needs to adjust for difference in the dates since each day represents a 24 hour difference that needs to be included. This is further complicated by having to deal with the time changes for DST, Day Light Savings Time, or Summer Time. This will add one hour in the fall sue the turn back of the clocks at 2:00 am.

Timesheets that use start and end times perform your calculation 7 times a week. Have you searched for "Timesheets"?

Yes, but not like that... Time calculations in JS are not simple.

Here's a good tutorial about the subject:

https://acrobatusers.com/tutorials/working-with-date-and-time-in-acrobat-javascript

https://acrobatusers.com/tutorials/working-with-date-and-time-in-acrobat-javascript-part-2

https://acrobatusers.com/tutorials/working-with-date-and-time-in-acrobat-javascript-part-3