can javascript read strings returned from app scri

Question

In Google-Apps-Script I have created a function which returns a string containing the id of a spreadsheet file (this id will vary from user to user, as it is a new file copied from a template).

function findSheet(){ 
//Opens User's Google Drive and searches files for a spreadsheet called "blahblah" and returns the active spreadsheet
var files = DriveApp.getFilesByName("blahblah");
var file = files.next();
var newID = file.getId();
Logger.log(newID);
return newID;
}

The Logger.log(newID) shows the id name of the file in my testing. However when I try to initiate a javascript variable to that returning id string it becomes undefined.

<script>
var idname;
idname = google.script.run.findSheet();
alert(idname);

I have another google scripts app function (which is called from javascript )which uses that id string variable as a parameter in order to write user input from my html page into their google spreadsheet as part as a web app, but the id name from the javascript goes in as undefined and the function does not work.

Is there something I do not know on why the apps script string is undefined when called on by javascript?

I tried using idname.toString() to fix but it still shows as undefined when i use an alert(idname) or document.write(idname) or rewriting a paragraph

<p idname="showmeID"></p>
<script>
document.showmeID.innerHTML.idname

Answer 1

google.script.run is an asynchronous client-side JavaScript API available in HTML-service pages that can call server-side Apps Script functions.

According to the documentation this API is asynchronous and does not return the value directly. Instead it returns the value in a callback function.

google.script.run
    .withFailureHandler(function(err){
        // callback function that will be executed when some error will occur.
        // Error object is passed as the first argument.
        console.log("failure handler", err)
    })
    .withSuccessHandler(function(res){
        // here withSuccessHandler runs when your findSheet function runs successfully.
        // value returned from google app script will be passed as the first argument of this callback function.
        // So you will receive the value returned from GAS in variable `res`.
        console.log("response from findSheet function", res)
    })
    .findSheet();