Blazor dictionary implementation of Local Storage

BrowserStorage.cs

using Microsoft.JSInterop;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Collections;

namespace Spin.Blazor
{
  public class BrowserStorage : IDictionary<string, string>
  {
    private static IJSInProcessRuntime _js;
    public BrowserStorageType Type { get; }
    private string _prefix;

    public BrowserStorage(BrowserStorageType type, IJSInProcessRuntime js)
    {
      Type = type;
      _js = js;
      _prefix = Type.ToString().ToLower() + "Storage";
    }

    public string this[string key]
    {
      get => _js.Invoke<string>($"{_prefix}.getItem", key);
      set => _js.Invoke<string>($"{_prefix}.setItem", key, value);
    }

    public string this[int index]
    {
      get => this[GetKey(index)];
      set => this[GetKey(index)] = value;
    }

    private string GetKey(int index) => _js.Invoke<string>($"{_prefix}.key", index);

    public ICollection<string> Keys => Enumerable.Range(0, Count).Select(x => GetKey(x)).ToList();
    public ICollection<string> Values => Enumerable.Range(0, Count).Select(x => this[GetKey(x)]).ToList();

    public int Count => _js.Invoke<int>("eval", $"{_prefix}.length");

    public bool IsReadOnly => false;

    public void Add(string key, string value)
    {
      if (ContainsKey(key))
        throw new ArgumentException("An element with the same key already exists");
      this[key] = value;
    }

    public void Add(KeyValuePair<string, string> item) => Add(item.Key, item.Value);

    public void Clear() => _js.InvokeVoid($"{_prefix}.clear");
    public bool Contains(KeyValuePair<string, string> item) => TryGetValue(item.Key, out var value) && item.Value == value;
    public bool ContainsKey(string key) => Keys.Contains(key);
    public void CopyTo(KeyValuePair<string, string>[] array, int arrayIndex) => Array.Copy(this.ToArray(), array, Count);

    public IEnumerator<KeyValuePair<string, string>> GetEnumerator()
    {
      for (int i = 0; i < Count; i++)
      {
        var key = GetKey(i);
        yield return new KeyValuePair<string, string>(key, this[key]);
      }
    }

    public bool Remove(string key)
    {
      if (!ContainsKey(key))
        return false;
      _js.InvokeVoid($"{_prefix}.removeItem", key);
      return true;
    }

    public bool Remove(KeyValuePair<string, string> item)
    {
      if (!Contains(item))
        return false;
      Remove(item.Key);
      return true;
    }

    public bool TryGetValue(string key, out string value)
    {
      value = this[key];
      return ContainsKey(key);
    }

    IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
  }
}