Preview deployment

Simulate a request against a function in Azion Console and read the response the code returns before the function serves traffic.

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Preview deployment runs a function in Azion Console and shows the response the code returns. It calls PreviewProvider, an auxiliary function in the source code that builds a simulated request and passes it to the handler. The output appears in the code editor, so you read the response before the function serves traffic.

PreviewProvider function

PreviewProvider is the entry point of a preview. It builds the request the preview sends, calls the function that processes that request, and returns the response the preview renders:

JavaScript
01function PreviewProvider(args) {
02 var request = new Request("https://www.azion.com/example", {
03 method: "GET",
04 headers: {
05 "Content-Type": "application/json",
06 "Authorization": "Bearer [TOKEN VALUE]"
07 },
08 redirect: "follow",
09 });
10 return handleRequest(request);
11}

The handler reads the properties of that request, so the values set inside PreviewProvider decide which path through the function runs.

Azion Console renders no preview while the source code carries no PreviewProvider function. The preview shows a warning that names the missing function.

Request simulation

Change the values inside PreviewProvider to exercise a different path through the function. A handler that branches on the request method returns HTML for a GET and JSON for a POST:

JavaScript
01const html = '<h1>Hello World</h1>'
02const data = { message: 'Hello World' }
03
04async function handleRequest(request) {
05 switch (request.method) {
06 case 'GET':
07 return new Response(html, {
08 headers: {
09 "content-type": "text/html",
10 }
11 })
12 case 'POST':
13 return new Response(JSON.stringify(data), {
14 headers: {
15 "content-type": "application/json",
16 }
17 })
18 }
19}

Each branch sets the content-type header for the format it returns. Switch the method inside PreviewProvider from GET to POST to read the other response.

Response rendering

The preview renders a response by its content-type header:

content-typePreview output
text/htmlThe HTML page, rendered.
application/jsonThe JSON body the function returns.

Azion Console shows the output in the code editor of the function. Select Open to show the same output in a separate browser tab. The inspect tool inside Preview deployment shows the behavior of the function in real time.

Functions quickstart

Create, instantiate, and run your first function end to end.

Code editor

Write the function whose response the preview renders.

Function instances

Bind the function to an application once the response is the one you want.

Troubleshooting

Find the cause when a function fails or returns nothing.

Query usage data from Functions

Read back the compute time and the invocations an account has consumed.