weekday(-dayOfWeek) goes back two weeks instead of 1

[ajenkinski]

Describe the bug
When I use the weekday plugin to find the previous instance of a day of the week, for example the last Sunday, it goes back two weeks instead of one. For example the documentation for the weekday plugin shows this example:

dayjs().weekday(-7); // last Sunday

which seems to indicate this would return the most recent Sunday. However the behavior I actually get is it returns the date of the Sunday before last.

Expected behavior

Here is a reproduction of the problem in the Node.js REPL.

> dayjs = require('dayjs')
> dayjs.extend(require('dayjs/plugin/weekday'))

> dayjs().format('YYYY-MM-DD')
'2021-01-14'
> dayjs().weekday(7).format('YYYY-MM-DD')
'2021-01-17'
> dayjs().weekday(-7).format('YYYY-MM-DD')
'2021-01-03'

As you can see, the current date when I ran this was 2021-01-14. I expected weekday(-7) to return the previous Sunday, 2021-01-10, but instead it returned 2021-01-03, which is the Sunday before the previous Sunday.

Information

• Day.js Version: v1.9.3
• OS: MacOS 10.15.7
• Browser: Node.js 12.5.0
• Time zone: GMT-05:00 EST

[iamkun]

This is the expected result.
As mentioned in doc

If the locale assigns Sunday as the first day of the week, dayjs().weekday(0) will be Sunday.

so, dayjs().weekday(-7) will be 7 days before Sunday

[ajenkinski]

Thanks. It makes sense to me now.