Local storage

🟨 Slightly different to Blazor Server

Local storage is a convenient and efficient way to store a small amount of data on the client-side, which can be easily accessed and updated by a web application.

• What is Local storage?
• Set up the base code for interacting with Local storage.
• Add common operations to your Local storage code.
• Use Local storage.
• Key differences between Blazor WebAssembly and Blazor Server.

You can download the example code used in this topic on GitHub.

What is Local storage?

Local storage is a modern technique that allows developers to store data in a key-value pair format. It can be thought of as a persistent browser dictionary with string-based keys and values. If non-string data is entered, it will be automatically converted to a string. For instance, if the key/value is set as the number 1, local storage will store it as a string "1". Data in local storage is isolated by domain, meaning that one domain cannot access another domain's resources. For instance, data created by blazorschool.com cannot be accessed by google.com and vice versa.

How to access the Local storage in the browser?

In Firefox, you can find the Local storage under the Storage tab, as shown in the image below:

In Chrome and Edge, you can find the Local storage under the Application tab, as shown in the images below:

Set up the base code for interacting with Local storage

The Local storage is exclusively accessible through the JavaScript API. This means that in order to access it, you will need to create a JavaScript module. You can refer to the JavaScript Interaction tutorial and choose between IJSRuntime or InteropServices.JavaScript to interact with your module. Below is an example of how to access the Local storage using IJSRuntime.

1. Create a new JavaScript file under the wwwroot folder. For example: /js/LocalStorageAccessor.js.
2. Create a C# class with the following base implementation:

public class LocalStorageAccessor : IAsyncDisposable
{
    private Lazy<IJSObjectReference> _accessorJsRef = new();
    private readonly IJSRuntime _jsRuntime;

    public LocalStorageAccessor(IJSRuntime jsRuntime)
    {
        _jsRuntime = jsRuntime;
    }

    private async Task WaitForReference()
    {
        if (_accessorJsRef.IsValueCreated is false)
        {
            _accessorJsRef = new(await _jsRuntime.InvokeAsync<IJSObjectReference>("import", "/js/LocalStorageAccessor.js"));
        }
    }

    public async ValueTask DisposeAsync()
    {
        if (_accessorJsRef.IsValueCreated)
        {
            await _accessorJsRef.Value.DisposeAsync();
        }
    }
}

3. Register the IndexedDbAccessor class in the Program.cs file:

builder.Services.AddScoped<LocalStorageAccessor>();

Add common operations to your Local storage code

In this section, we will demonstrate how to perform basic Local storage operations in JavaScript and C#. With the provided code, you can easily store, get, and delete data from the Local. Additionally, you can customize the code to add your own operations as well.

1. To store, get and delete data, add the following functions to your JavaScript module:

export function get(key)
{
    return window.localStorage.getItem(key);
}

export function set(key, value)
{
    window.localStorage.setItem(key, value);
}

export function clear()
{
    window.localStorage.clear();
}

export function remove(key)
{
    window.localStorage.removeItem(key);
}

2. To use these operations in your C# class, add a method for each operation, and call WaitForReference() in all of them. Here is an example implementation:

public class LocalStorageAccessor : IAsyncDisposable
{
    ...
    public async Task<T> GetValueAsync<T>(string key)
    {
        await WaitForReference();
        var result = await _accessorJsRef.Value.InvokeAsync<T>("get", key);

        return result;
    }

    public async Task SetValueAsync<T>(string key, T value)
    {
        await WaitForReference();
        await _accessorJsRef.Value.InvokeVoidAsync("set", key, value);
    }

    public async Task Clear()
    {
        await WaitForReference();
        await _accessorJsRef.Value.InvokeVoidAsync("clear");
    }

    public async Task RemoveAsync(string key)
    {
        await WaitForReference();
        await _accessorJsRef.Value.InvokeVoidAsync("remove", key);
    }
}

Use Local storage

Once you have completed all the previous steps, you can use the Local storage as follows:

@inject LocalStorageAccessor LocalStorageAccessor

<h3>BrowserStorageDemonstrate</h3>
<form>
    <label>
        Key
        <input type="text" @bind-value="Key" />
    </label>
    <label>
        Value
        <input type="text" @bind-value="Value" />
    </label>
    <button type="button" @onclick="SetValueAsync">Set Value</button>
</form>
<div>Stored Value: @StoredValue</div>
<button type="button" @onclick="GetValueAsync">Get Value</button>
<button type="button" @onclick="RemoveAsync">Remove Value</button>
<button type="button" @onclick="ClearAllAsync">Clear All</button>

@code {
    public string Key { get; set; } = "";
    public string Value { get; set; } = "";
    public string StoredValue { get; set; } = "";

    public async Task SetValueAsync()
    {
        await LocalStorageAccessor.SetValueAsync(Key, Value);
    }

    public async Task GetValueAsync()
    {
        StoredValue = await LocalStorageAccessor.GetValueAsync<string>(Key);
    }

    public async Task RemoveAsync()
    {
        await LocalStorageAccessor.RemoveAsync(Key);
    }

    public async Task ClearAllAsync()
    {
        await LocalStorageAccessor.Clear();
    }
}

Key differences between Blazor WebAssembly and Blazor Server

In Blazor Server, you can only use IJSRuntime to interact with the JavaScript. In addition, to access Local storage, developers can use the ProtectedLocalStorage class.