How to access native JS object as a Map<String, Any>?

JavaScript
1

In JS, if there is an array in the native layer, I can use it in kotlin as an Array<T>.  How can I do a similar thing with maps/objects? If I try something like this:

  val m: Map<String, Any> = …
  for (k in m.keySet()) {  …  }
  m[“foo”]

where m is a object in native JS, keySet etc is undefined.

Rob

2

Right way to do it now is cast object to Json, but it's not map.

3

If you really want to get Map you can wrap your object by Map implementation from stdlib, like:

import java.util.HashMap

fun <V> PrimitiveHashMap(container: dynamic): HashMap<String, Any> {
    val m = HashMap<String, Any>().asDynamic()
    m.map = container
    val keys = js("Object.keys")
    m.`$size` = keys(container).length
    return m
}

fun main(args: Array<String>) {
    val e = PrimitiveHashMap<Int>(js("({})"))
    println(e)
    
    val m = PrimitiveHashMap<Int>(js("({aaa: 1, bbb: 2})"))
    println(m)
}

But note, please, it is hack which depends to implementation details and they can be changed in the future.

I created issues(KT-5653, KT-5654) which covered this, feel free to vote or star them for get updates.

2 Likes
4

Great, thanks!

5

Looks like this hack no longer works. Is there an updated version?

Rob

6

I updated answer

7

Shouldn’t this be inside the JS stdlib?

2 Likes
8

Another way is just to iterate over the key-value pairs of a JS object:

fun entriesOf(jsObject: dynamic): List<Pair<String, Any?>> =
    (js("Object.entries") as (dynamic) -> Array<Array<Any?>>)
        .invoke(jsObject)
        .map { entry -> entry[0] as String to entry[1] }

fun mapOf(jsObject: dynamic): Map<String, Any?> =
    entriesOf(jsObject).toMap()
3 Likes