Map.set really really slow

Map.set is really slow for me. Taking 14.677 seconds to set 300-400 items. I’m using Chrome for testing.

I’ve created a custom Map object:

export class DataMap<T> extends Map<string, T> {
  constructor(...args:MapConstructorParameters){
    super(...(args as []))
  }
  updateFromList(values:any[], {key='id', sortKey=null} : UpdateFromListOptions){
    // const self = this;

    let _values:any[];
    if (sortKey){
      console.log('Sorting')
      _values = this._sortValues(values, sortKey) // implementation not shown for brevity
      console.log('Sorting Finished')
    } else {
      _values = []
    }

    console.log('Setting')
    _values.forEach((_:any)=>{
      this.set(_[key], _ as T)
    })
    console.log('Setting finished')

  }
}

The idea of updateFromList is a little bit of syntax sugar, to allow passing of a list of objects and append them by a ‘key’ to the map. The part that is really slow is this:

    console.log('Setting')
    _values.forEach((_:any)=>{
      this.set(_[key], _ as T)
    })
    console.log('Setting finished')

Is this use of the Map a no go or am doing something stupid here?