Support for Dependency injection begins with Azure Functions 2.x which means Dependency Injection in Azure function can now leverage .NET Core Dependency Injection features.

Before you can use dependency injection, you must install the following NuGet packages:

• Microsoft.Azure.Functions.Extensions
• Microsoft.NET.Sdk.Functions

Having Dependency Injection eases things like DBContext, Http client usage (Httpclienfactory), Iloggerfactory, cache support etc.

Firstly, update the Startup class as shown below

namespace DemoApp
{
    public class Startup: FunctionsStartup
    {
        public override void Configure(IFunctionsHostBuilder builder)
        {
            builder.Services.AddScoped<IHelloWorld, HelloWorld>();

            // Registering Serilog provider
            var logger = new LoggerConfiguration()
                .WriteTo.Console()
                .CreateLogger();
            builder.Services.AddLogging(lb => lb.AddSerilog(logger));
            //Reading configuration section can be added here etc.
        }
    }
}

Secondly, Removal of Static keyword in Function class and method level

public class DemoFunction
{
    private readonly IHelloWorld _helloWorld;
    public DemoFunction(IHelloWorld helloWorld)
    {
        _helloWorld = helloWorld;
    }

    [FunctionName("HttpDemoFunction")]
    public async Task<IActionResult> Run(
        [HttpTrigger(AuthorizationLevel.Anonymous, "get", "post", Route = null)] HttpRequest req,
        ILogger log)
    {
        log.LogInformation("C# HTTP trigger function processed a request.");
    }

If we look into above e.g. IHelloWorld is injected using .NET Core DI

**Note:**In-spite of having latest version of Azure function v3 for Dependency Injection to enable few steps are manual as shown above

Sample code on github can be found here