Sending Data From Javascript to FastAPI

How do I send data from client (javascript) to my server (python fastapi)? I am having trouble understanding the format that I need my data in. I have this “simple” example that I’ve been trying to get working to help me understand what is happening.

    document.getElementById('submitButton').addEventListener('click', async (event) => {
        event.preventDefault();

        const formData = new FormData();
        formData.append('input_data', 'I am working');

        try {

            const response = await fetch('/function/', {
                method: 'POST', 
                body: formData
            });

            const result = await response.json();
            if (response.ok) {
                console.log('Response ok');
            } else {
                console.log('Response not ok');
            }


        } catch (error) {
            console.log('error');
        }
    });

@app.post('/function/')
async def function(input_data: str = Form(...)):
    print(input_data)
    return {'message': 'Success!'}