parse javascript date to elixir format - date

Question

I have some saved dates in JavaScript using new Date() that looks like:
"Sun Feb 24 2019 14:44:20 GMT+0200 (Eastern European Standard Time)"
I'm trying to parse these to Elixir DateTime; I didn't find anything in "timex" that can help and I already know that I can use DateTime.from_iso8601 but for dates saved using new Date().toISOString() but what i need is to parse the above string.
Thanks in advance

Answer 1

You can use elixir binary pattern matching to extract the date parts and parse using Timex's RFC1123 format. The RFC1123 is the format e.g Tue, 05 Mar 2013 23:25:19 +0200. Run h Timex.Format.DateTime.Formatters.Default in iex to see other formats.
iex> date_string = "Sun Feb 24 2019 14:44:20 GMT+0200 (Eastern European Standard Time)"
iex> <<day_name::binary-3,_,month_name::binary-3,_,day::binary-2,_,year::binary-4,_,time::binary-8,_::binary-4,offset::binary-5,_,rest::binary>> = date_string
iex> Timex.parse("#{day_name}, #{day} #{month_name} #{year} #{time} #{offset}", "{RFC1123}")
iex> {:ok, #DateTime<2019-02-24 14:44:20+02:00 +02 Etc/GMT-2>}
Pattern matching:
The binary-size are in byte sizes. 1 byte == 1 character. For instance to get
3-character day_name the size is 3. Underscores (_) is used to pattern match the spaces in the date format
Updated answer to use binary-size rather than bitstring-size for simplicity

Answer 2

I didn't find anything in "timex" that can help
The Timex Parsing docs say that you can use strftime sequences, e.g %H:%M:%S, for parsing. Here's a list of strftime characters and what they match.
Here's a format string that I think should work on javascript Dates:
def parse_js_date() do
Timex.parse!("Sun Feb 24 2019 14:44:20 GMT+0200 (Eastern European Standard Time)",
"%a %b %d %Y %H:%M:%S GMT%z (%Z)",
:strftime)
end
Unfortunately, %Z doesn't want to match the time zone name, which causes Timex.parse!() to spit out an error. It looks like %Z in Elixir only matches one word, e.g. a timezone abbreviation EET. Therefore, my simple, clean solution is spoiled.
What you can do is chop off the time zone name before parsing the date string:
def parse_js_date_string() do
[date_str|_tz_name] = String.split(
"Sun Feb 24 2019 14:44:20 GMT+0200 (Eastern European Standard Time)",
" (",
parts: 2
)
Timex.parse!(date_str,
"%a %b %d %Y %H:%M:%S GMT%z",
:strftime)
end
In iex:
~/elixir_programs/my$ iex -S mix
Erlang/OTP 20 [erts-9.3] [source] [64-bit] [smp:4:4] [ds:4:4:10] [async-threads:10] [hipe] [kernel-poll:false]
Compiling 1 file (.ex)
Interactive Elixir (1.6.6) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> My.parse_js_date_string()
#DateTime<2019-02-24 14:44:20+02:00 +02 Etc/GMT-2>
iex(2)>