Add new set function

[jmannanc]

Fix #1388

Moment.js also has a function like this one so I thought it'd be good to add, and may be easier for some people to use.
This is my first contribution so do let me know if I did anything wrong and I'll be happy to fix it.

[jmannanc]

I keep getting flow errors if I try to implement tests to check for the types. Are these tests/RangeErrors unneeded then?

[leshakoss]

@sneakyfish5 thank you for the contribution! We'd want to see this function in the library, please check the review comments out

[leshakoss]

I keep getting flow errors if I try to implement tests to check for the types. Are these tests/RangeErrors unneeded then?

You need to let flow know about the intended type mismatch: https://github.com/date-fns/date-fns/blob/master/src/areIntervalsOverlapping/test.js#L166

[leshakoss]

@sneakyfish5 Thanks a lot! 🙏 I've got some new comments and nitpicks, please check them out

[leshakoss]

I meant this not only for months but for every value. Like for instance you could have negative years (ie years BC) and they will be treated by this function just like null.

What I think we need to do is to check for nullability and set the value right away for every value instead of the useless > 0 intermediate check.
I suggest consolidating it all like this:

if (values.year != null) {
  date.setFullYear(toInteger(values.year))
}

if (values.month != null) {
  date.setMonth(toInteger(values.month))
}

if (values.date != null) {
  date.setDate(toInteger(values.date))
}

and so on. (Braces are fine, they don't affect the bundle size)

[jmannanc]

Fixed, however I needed to keep days for the setMonth otherwise it would create an error where the resulting month is a month higher than it is supposed to be. Maybe my implementation is wrong, however I saw this happening date-fns setMonth function as well, so I opted to leave it in there unless you have any objection.

[leshakoss]

Not sure what do you mean. I checked the branch out locally and removed daysForMonth and tests pass, also in the console it looks normal:

> const set = require('./src/set')
> set(new Date(), {month: 0}).toString()
'Sun Jan 06 2019 13:24:19 GMT+0100 (Central European Standard Time)'

What am I missing?

[jmannanc]

Huh, I'm not too sure. When I run the tests on my local with daysForMonth removed I end up failing this test, and using daysForMonth as the extra parameter seemed to fix it.

    × set the date with every option
      Chrome 76.0.3809 (Windows 10.0.0)
    AssertionError:   # src\set\test.js:18
      
      assert.deepEqual(result, new Date(2014, 8, 20, 12, 12, 12, 12))
                       |       |
                       |       new Date("2014-09-20T17:12:12.012Z")  
                       new Date("2014-10-20T17:12:12.012Z")

Maybe I've messed up something on my end?

[leshakoss]

@sneakyfish5 I removed daysForMonth from your branch just to let travis do the full test run through the time zones, let's see what the bug is

[jmannanc]

It failed, but I'm not quite sure the reason behind it failing or not/why it's only for that test.

[leshakoss]

@sneakyfish5 ok, I added an import of setMonth like you did before and seems like the bug is gone. Let's see what will travis say about this :)

Also done some minor stylistic changes to make the code a bit more uniform with the rest of date-fns.

[leshakoss]

@sneakyfish5 alright I think it's ready to be merged. Thanks a lot for your contributon! ⭐️

[jmannanc]

Awesome, thank you @leshakoss for all the help. I squashed the commits for cleanup.

[kossnocorp]

Looks good, thank you a lot!