What Bernd meant earlier is that your script is basically missing an important part of this calculation.
The first thing I noticed is the same observation as Gkaiseril.
You cannot use AM/PM format if you're using military time format, that is a 24 hour period.
In AM/PM format you deal with hours 1 through 12 and the AM or PM indicator lets you know if it is morning or evening times. In military time format you deal with 24 hour period. Formats are not expressed as 9:00 for example, It has the extended "0" for hours and minutes. Morning begins at 00:00 while Midnight end at 24:00 not 12:00 for example.
So, for example, you will run into conflict with your script because 12:30 (at noon) - 21:05 (9:05 PM) is not greater than the end time.
To do it correctly it will have to be expressed like this:
If starting minutes are greater than the minutes of ending time just substract hours and add the minutes normally (a resulting negative value of the hours shouldn't matter to us, but will will matter in you javascript equation(s) though. So pay attention to those negative totals.
If starting minutes are not greater than the minutes of the ending time, then follow the rule of thumb:
Substract one hour from the ending time hours.
Add 60 minutes to the starting time minutes, then substract the total hours and minutes
That would be the toal in hours and minutes between the two times.
See more here how to do it manually: How To Add and Subtract Time in Hours and Minutes
Your current script not only disregards what happens when the starting time is less than the ending time, but also, disregards what happen in the event that would normally take place at noon (12:00) versus midnight (24:00).
And since you've splitted the resulting hours and minutes as separate strings Bernd pointed out that your script is incomplete, because is missing a basic time arithmetic formula.
When the time is expressed in a numerical manner to substract hour and minutes between two given times, if the hour and minutes of the starting time are less than the hours and minutes of the ending time, you need to use this equation: https://www.aaamath.com/B/meatsbhm.htm
Look in the example in that website. It says:
What is 4 hours 11 minutes minus 2 hours 47 minutes.
The original number of minutes (11) is less than the 47 minutes being subtracted so:
Subtract 1 from the original number of hours. (4 hours - 1 hour = 3 hours)
Increase the number of minutes by 60. (11 minutes + 60 minutes = 71 minutes)
Subtract the minutes. (71 minutes - 47 minutes = 24 minutes)
Subtract the hours. (3 hours - 2 hours = 1 hour)
Answer: 1 hour 24 minutes
Using the arithmetic rule posted above, the part you should be looking to fix in your script is here:
var hourDiff = Math.abs(finishArr[0] - startArr[0]);
var minDiff = Math.floor((Math.abs(finishArr[1] - startArr[1]) / 60)*60);
You may need to also implement a conditional statement, like Bernd spotted. See this this other part in your script:
if (start1!="" && finish1!="") {
It should provide a condition to handle what happens if the starting time is not greater than the ending time, because if it's not, then you have to consider the rule of thumb of substracting 1 from the total hours of the ending time, then add 60 to the total number of minutes of the starting time. Only then you'll be able to totalize correctly. So consider something like:
// declare all your variables first
if ( (startArr !="" && finishArr !="") {
// state a condition to handle what happens if the starting time is less than the ending time
if (start1.length < finish1.length) {
// then put your code here
} else {
// do something else or declare no result to display if the conditions above are not met.
//For example, if starting time is greater than ending time then do
if (start1.length > finish1.length) {
//and put the code here to handle that condition
}
}
}
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