Blazor WASM apps communicate with backend APIs using HttpClient. The System.Net.Http.Json extension methods make JSON calls concise and type-safe.

Registering HttpClient

// Program.cs
builder.Services.AddScoped(sp =>
    new HttpClient { BaseAddress = new Uri(builder.HostEnvironment.BaseAddress) });

GET Request

@inject HttpClient Http

protected override async Task OnInitializedAsync()
{
    products = await Http.GetFromJsonAsync<List<Product>>("/api/products");
}

POST Request

var response = await Http.PostAsJsonAsync("/api/products", newProduct);
if (response.IsSuccessStatusCode)
{
    var created = await response.Content.ReadFromJsonAsync<Product>();
}

PUT and DELETE

await Http.PutAsJsonAsync($"/api/products/{id}", updated);
await Http.DeleteAsync($"/api/products/{id}");

Error Handling

try
{
    data = await Http.GetFromJsonAsync<List<Item>>("/api/items") ?? new();
}
catch (HttpRequestException ex)
{
    errorMessage = ex.Message;
}

Reference:

Wikipedia: REST

https://en.wikipedia.org/wiki/Representational_state_transfer