+++
title = "Define the HitCounter API"
weight = 100
+++

## Create a new file for our hit counter construct

Create a new folder called `hitcounter` and name a new file `hitcounter.go` with the following content:

```ts
package hitcounter

import (
	"github.com/aws/aws-cdk-go/awscdk/v2/awslambda"
	"github.com/aws/constructs-go/constructs/v10"
)

type HitCounterProps struct {
  // Downstream is the function for which we want to count hits
	Downstream awslambda.IFunction
}

type hitCounter struct {
	constructs.Construct
}

type HitCounter interface {
	constructs.Construct
}

func NewHitCounter(scope constructs.Construct, id string, props *HitCounterProps) HitCounter {
	this := constructs.NewConstruct(scope, &id)

	return &hitCounter{this}
}
```

Save the file. This doesn't do anything for now, but we'll be completing this file shortly.

## What's going on here?

* We declared a new construct function called `NewHitCounter` which will return
  a `HitCounter`.
* As usual, arguments for constructs are `scope`, `id` and `props`.
* The `props` argument is of type `HitCounterProps` which includes a single
  property `downstream` of type `awslambda.IFunction`. This is where we are going to "plug in" the
  Lambda function we created in the previous chapter so it can be hit-counted.

----

Next, we are going to write the handler code of our hit counter.