How to create a Date object and subtract days from...

# javascript

[Alexander Weickmann]

How to create a Date object and subtract days from it?
In JS, the accepted solution is:

var d = new Date();
 d.setDate(d.getDate()-5);

But the Kotlin JS Date object does not expose setDate ...

[Lawik]

You could use dynamic:

var d = new Date()
d.asDynamic().setDate(d.getDate()-5)

[Lawik]

Probably better to write an extension function for Date

[Lawik]

fun main() {
    val date = Date()
    date.setDate(4)
}

fun Date.setDate(date: Int){
    this.asDynamic().setDate(date)
}

[Alexander Weickmann]

works! Thx a lot 🙂

[Lawik]

Should probably report the issue on https://youtrack.jetbrains.com though, since the set functions are part of Date.

[ilya.gorbunov]

We have intentionally avoided providing mutating methods on Date.

[thana]

why?

[ilya.gorbunov]

We believe having a mutable date is not a good approach for working with dates. So we avoid promoting this way in Kotlin/JS. Though the workaround is easy when absolutely required.

[thana]

while this is true do you really think you should do this dicission when the api is actually not under your control? 😕

[ilya.gorbunov]

The way we expose Date in kotlin.js package is definitely under our control. It's the same thing as with js Math API, for example: currently we're deprecating it in favor of kotlin.math package.

[cfnz]

I have found (but have not yet used) a cross platform date library that looks really good... https://korlibs.soywiz.com/klock/ (there are also a few other interesting things on that site...)