Alright, let's break down exactly how the control flow works between your Google Sheets-bound Apps Script server-side functions and those client-side modal/non-modal dialogs—since you already have the basic google.script.run call working, this should clarify every step behind the scenes.

First, let's anchor this to the code snippet you're already using successfully:

google.script.run.withSuccessHandler(success_callback).getCredentials(this.parentNode)

Here's the play-by-play of what happens from the moment this line fires until your success callback runs:

1. Client-Side Trigger & Request Launch #

• When a user interacts with your dialog (clicks a button, selects an option, etc.), this line executes in the dialog's browser-based JavaScript context.
• google.script.run is Google's built-in bridge that connects the dialog's client-side code (running in the user's browser) to the Apps Script runtime (hosted on Google's servers—not the user's machine).
• Chaining .withSuccessHandler(success_callback) tells the client: "Once the server sends back a successful response, run this success_callback function with the returned data."
• The final .getCredentials(this.parentNode) sends the data from this.parentNode (your dialog's DOM element context) as a parameter to your server-side getCredentials function.

2. Server-Side Execution #

• The request hits Google's Apps Script servers, which spin up a runtime instance for your bound sheet script (if one isn't already active).
• The server runs your getCredentials function with the data you passed from the client. A few critical notes here:
  • This runs asynchronously—your dialog won't freeze while the server works. For modals, the user can't interact with the underlying sheet, but they can still interact with the dialog itself; for non-modals, they can use both the sheet and dialog during this time.
  • The server-side function has full access to your Google Sheet (via SpreadsheetApp) and other Apps Script services—this is why you're using it to fetch credentials in the first place.
  • Pro tip: You should add a .withFailureHandler(error_callback) chain here too—this will catch server-side errors (like permission issues or invalid data) and let you handle them gracefully in the dialog.

3. Response Handoff to Client #

• Once getCredentials finishes running, the server sends the function's return value back to the user's browser.
• If the execution was successful, the client immediately triggers your success_callback function, passing the server's return value as an argument. This is exactly why your current callback is working—this is the handoff point where server data gets injected back into your dialog's UI.
• If there was an error, the failure handler (if you set it up) will run instead, giving you details about what went wrong.

Key Control Flow Rules to Keep in Mind #

• No blocking client code: google.script.run is asynchronous by design. Any code you write right after your google.script.run line will execute immediately, before the server responds. Never try to use the server's return value right after the call—you must wait for the success handler.
• Data passing limits: You can send primitive values (strings, numbers, booleans), arrays, and plain objects between client and server. You can't pass DOM elements directly (which is why you're passing this.parentNode's data instead of the element itself—great call!).
• Modal vs non-modal doesn't change the flow: The only difference between modal and non-modal dialogs is whether the user can interact with the underlying sheet. The back-and-forth between client dialog code and server-side script works exactly the same for both.

Quick Example to Tie It All Together #

Suppose your server-side function looks like this:

function getCredentials(elementData) {
  // Use the passed data to fetch credentials from the sheet
  const sheet = SpreadsheetApp.getActiveSpreadsheet().getActiveSheet();
  const credentials = sheet.getRange(elementData.dataset.row, 2).getValue();
  return credentials;
}

And your client-side success callback is:

function success_callback(credentials) {
  // Update the dialog's UI with the fetched credentials
  document.getElementById('credential-display').textContent = credentials;
}

The full flow is:

1. User clicks a button → google.script.run sends this.parentNode's data to the server.
2. Server runs getCredentials, pulls the credential value from the sheet, and sends it back.
3. Client receives the credential, runs success_callback, and updates the dialog to show the value.

That's the complete loop! Let me know if you want to dive deeper into any specific edge case or part of the flow.

内容的提问来源于stack exchange，提问作者P Burke