Element: [Bug Report] While using 'value-format' in date-range-picker and giving value ['', ''], it resets to 1970-01-01

[docodocool]

Element UI version

2.4.0

OS/Browsers version

Win10 Chrome66 x64

Vue version

2.5.17-beta.0

Reproduction Link

https://jsfiddle.net/coolucifer/nw9v5fux/35/

Steps to reproduce

create a el-date-picker and set value-format="yyyy-MM-dd", v-model a value equals ['', ''], click the date-picker

What is Expected?

just like other date-picker it shows this month and next month

What is actually happening?

it shows 1970-01 and 1970-02

[wacky6]

empty value must be falsy, such as null, "". Array with empty strings are considered non-empty

[docodocool]

@wacky6 when i click the date-range-picker without 'value-format' v-modeled ['', ''] it shows this month and next month, while the date-picker with 'value-format' shows 1970. is that a bug?

https://jsfiddle.net/coolucifer/nw9v5fux/40/

[w514986768]

我也遇到了这个问题

[wacky6]

As said, use null or "" to represent empty value. Using array will not work, and this is intentional, to remain consistent with other component.

"''" is parsed to 1970-1-1 internally.

[docodocool]

@wacky6 well...i wonder why it presents two results on two date-range-pickers, is it deliberately to make it 1970 on date-range-picker with 'value-format: 'yyyy-MM-dd'?

[wacky6]

What do you mean by two results. The internal parser just happens to parse empty string to that value.

[docodocool]

@wacky6 https://jsfiddle.net/coolucifer/nw9v5fux/40/ in this page there are two date-pickers, one has 'value-format' and another doesn't, they are binded the same value '['', '']', but when i click each date-picker it shows different calendars.
this is the one with 'value-format', it shows 1970-01 and 1970-02:

and here is the another one without 'value-format', it shows this month and next month:

is it caused by 'value-format' or sth else?

[wacky6]

Yes. value-format will result in the value being parsed / formatted.

[docodocool]

@wacky6 thank you for your reply. Now i watch value binds date-picker with 'value-format' and when i clear date-pickers, i will set the value [] from null(for ['', ''] will reset the calendar to 1970). At the same time i try to get beginDate by value[0], and endDate by value[1], it has errors for there is no value[1], i have to validate it everytime when the value changes, it's a little stupid. Is it possible to make date-picker binded ['', ''] with 'value-format' and without 'value-format' have the same performance?

[wacky6]

In that case, you need to wrap your own component.

[docodocool]

OK, thanks.