The request.json() method in Astro already returns the body of the request as a JavaScript object. When you do const body: Order[] = await request.json();, you're parsing the JSON body of the request into a JavaScript object and storing it in the body variable.
If the body of your request is a JSON array of Order objects, request.json() will return that array as a JavaScript array of objects. Here's an example:
export const POST: APIRoute = async ({{ request }}) => {{
try {{
const body: Order[] = await request.json();
}} catch (error) {{
}}
}}
In this example, if the body of your request is [{ "id": "product1", "quantity": 2 }, { "id": "product2", "quantity": 3 }], body will be [{ id: "product1", quantity: 2 }, { id: "product2", quantity: 3 }].
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