Date.day_of_week

You're seeing just the function day_of_week, go back to Date module for more information.
Link to this function

day_of_week(date, starting_on \\ :default)

View Source (since 1.4.0)

Specs

day_of_week(Calendar.date(), starting_on :: :default | atom()) ::
  Calendar.day_of_week()

Calculates the day of the week of a given date.

Returns the day of the week as an integer. For the ISO 8601 calendar (the default), it is an integer from 1 to 7, where 1 is Monday and 7 is Sunday.

An optional starting_on value may be supplied, which configures the weekday the week starts on. The default value for it is :default, which translates to :monday for the built-in ISO calendar. Any other weekday may be given to.

Examples

iex> Date.day_of_week(~D[2016-10-31])
1
iex> Date.day_of_week(~D[2016-11-01])
2
iex> Date.day_of_week(~N[2016-11-01 01:23:45])
2
iex> Date.day_of_week(~D[-0015-10-30])
3

iex> Date.day_of_week(~D[2016-10-31], :sunday)
2
iex> Date.day_of_week(~D[2016-11-01], :sunday)
3
iex> Date.day_of_week(~N[2016-11-01 01:23:45], :sunday)
3
iex> Date.day_of_week(~D[-0015-10-30], :sunday)
4