How to define number of decimals in Kotlin/JS and Kotlin/Wasm?

Question

Let's imagine something like this:

var num: Float = 0.0f
num = 2.4 * 3.5 / 3.8

num has several decimals, but I want only 2.

In JS I would use num.toFixed(2).

Other answers here suggest to use "%.2f".format(num) or num.format(2). The latter needs a custom extension function:

fun Double.format(digits: Int) = java.lang.String.format("%.${digits}f", this)

However, any of these options leads to a compiler error of "unresolved reference". I don't think it is a question of imports because the compiler would suggest it.

Is there an easy way to do this?

Croner

Did I understand correctly that you try to compile Kotlin to JS? – Heavenward

Yes, that is what they're doing. – Barbarity

Related: https://mcmap.net/q/839817/-is-there-a-way-in-kotlin-multiplatform-to-format-a-float-to-a-number-of-decimal-places/8583692 – Punke

Answer 1

Kotlin standard library for JS doesn't have anything like Double.format yet, but you can implement it easily with aforementioned toFixed function available in javascript:

fun Double.format(digits: Int): String = this.asDynamic().toFixed(digits)
fun Float.format(digits: Int): String = this.asDynamic().toFixed(digits)

This works because Double and Float in Kotlin are represented with Number data type in JS, so you can call toFixed() function on instances of those types.

Wreathe

Nice! That worked, thanks! However you mistake in call toFixed(), you have to call format(). So in my example would be num.format(2). To be said also that this also convert Float to String, so better called when have to print it – Croner

Answer 2

For Kotlin/Wasm, this is how it can be done.
Note that the function return type should be kotlin.js.JsNumber:

val myValue = 0.12345f
val myValue2Decimals = roundTo2Decimals(myValue)

fun roundTo2Decimals(number: Float): JsNumber = js("number.toFixed(2)")

Punke