How to get the specific range of row data from google sheet through apps script

I thought that in your case, the retrieved values might be required to be modified. So how about the following modification? In your script, the values are retrieved from the column "A". So, this is also reflected to the modified script.

Modified script:

When your script is modified, please modify as follows.

var rows = sheet.getRange(from,1,from+where, sheet.getLastColumn()).getValues();

var rows = sheet.getRange(from, 1, where, 1).getValues();

and

var rows = sheet.getRange(from,1,sheet.getLastRow()-1, sheet.getLastColumn()).getValues();

var rows = sheet.getRange(from, 1, sheet.getLastRow() - from + 1, 1).getValues();

Or, as other pattern, how about the following sample script?

Sample script 1:

In this sample, your getUsers is modified. In this pattern, the range is changed for from and where and the values are retrieved from the specific range.

function getUsers(sheet,request){
  var from = request.parameter.from;
  var where = request.parameter.where;
  
  const values = sheet.getRange(from, 1, sheet.getLastRow() - from - where >= 0 ? where : sheet.getLastRow() - from + 1, 1).getValues();
  const result = JSON.stringify({user: values.map(([a]) => ({ProductId: a}))});
  return ContentService.createTextOutput(result).setMimeType(ContentService.MimeType.JSON);
}

Sample script 2:

In this sample, your getUsers is modified. In this pattern, all values are retrieved for the column "A" and the specific values are retrieved using splice. In this case, from and where can be directly used. I think that this might be the same flow with Frank's comment.

function getUsers(sheet,request){
  var from = request.parameter.from;
  var where = request.parameter.where;
  
  const values = sheet.getRange(1, 1, sheet.getLastRow(), 1).getValues().splice(from, where);
  const result = JSON.stringify({user: values.map(([a]) => ({ProductId: a}))});
  return ContentService.createTextOutput(result).setMimeType(ContentService.MimeType.JSON);
}

Note:

• When you modified the script, please redeploy the Web Apps as new version. By this, the latest script is reflected to Web Apps. Please be careful this.

References:

• getRange(row, column, numRows, numColumns)
• splice()

Added:

When the columns are 3 columns like "ProductId", "ProductName" and "ProductImage", the sample script 1 and 2 is as follows.

From:

const values = sheet.getRange(from, 1, sheet.getLastRow() - from - where >= 0 ? where : sheet.getLastRow() - from + 1, 1).getValues();
const result = JSON.stringify({user: values.map(([a]) => ({ProductId: a}))});

To:

const values = sheet.getRange(from, 1, sheet.getLastRow() - from - where >= 0 ? where : sheet.getLastRow() - from + 1, sheet.getLastColumn()).getValues();
const result = JSON.stringify({user: values.map(([a,b,c]) => ({ProductId: a: ProductName: b, ProductImage: c}))});

or

From:

const values = sheet.getRange(1, 1, sheet.getLastRow(), 1).getValues().splice(from, where);
const result = JSON.stringify({user: values.map(([a]) => ({ProductId: a}))});

To:

const values = sheet.getRange(1, 1, sheet.getLastRow(), sheet.getLastColumn()).getValues().splice(from, where);
const result = JSON.stringify({user: values.map(([a,b,c]) => ({ProductId: a: ProductName: b, ProductImage: c}))});

• When you want to expand this, please modify [a,b,c] to [a,b,c,d,e,f,,,] and {ProductId: a: ProductName: b, ProductImage: c} to {ProductId: a: ProductName: b, ProductImage: c, key1: d, key2: e, key3: f}.

Here's a start at a refactor. A few things I don't understand and need clarification on:

1. Why are you adding from and where for the loop? If I set from=10; where=20, I get results from 10 through 39. I'm guessing that is not what you want.
2. Obviously you'll want to clean up the default values for myfunc.

function doGet(request)
{
  return myfunc(request.parameter.from, request.parameter.where);
}

function myfunc(from=10, where=20){
  let sheet = SpreadsheetApp.openById("1CP1n-B87RD_BfffrOKVemmbqQ4-rq3W5t59x90tX0VA").getSheetByName("Products");
  var jo = {user:[]};

  const rawdata = sheet.getRange(1, 1, sheet.getLastRow(), sheet.getLastColumn()).getValues();
  const data = rawdata.slice(from, where);
  
  data.map((row, idx, arr)=>{
     let record = {};
     record['ProductId'] = row[0];
     jo.user.push(record);
  });

  return JSON.stringify(jo);
}