isNaN

Returns true if the specified number is a Not-a-Number (NaN) value, false otherwise.

expect fun Double.isNaN(): Boolean(source)

fun main() {
    val normal = 42.0
    val nan    = 0.0 / 0.0      // produces NaN

    println("normal.isNaN() = ${normal.isNaN()}") // false
    println("nan.isNaN()    = ${nan.isNaN()}")     // true
}

Source