Immutable Record with an immutable List member

record.js

(() => {
const {List, Record} = require("immutable")
class Foo extends Record({ list: List() }) {
  constructor( props ) {
    const inst = super( props )
    const list = inst.get( "list" )
    if( list instanceof Array ) {
      return inst.set( "list", List( list ) )
    }
    if( !List.isList( list ) ) { throw new Error ( "List member should be type List, or Array" ) }
  }
}
assert.ok( List.isList((new Foo()).get("list")) )
assert.ok( List.isList((new Foo( {list: ["one"]} )).get("list")) )
assert.throws( () => new Foo( {list:""} ) )
})()