Find matching text in sheets - google-apps-script

Question

At a charity, volunteers are issued i.d. cards with QR codes. To clock in, a volunteer scans their i.d. card. A script automatically inserts the person's name into column 1 of a Google Sheet and inserts a timestamp into column 2 of the same row, to indicate timeIn. Next, we want to automate clocking out.
When a person's i.d. card is scanned, I know how to insert the person's name into a temporary holding cell. Next, I need code to check whether that person has already signed in (i.e., compare contents of the holding cell to each cell in column 1 until a match or an empty cell is found). If a match is found, then a timestamp should be entered in column 3, in the row where the person signed in, to indicate timeOut. Then, data in the temporary holding cell should be cleared.
I am very new to scripts for google apps, and have not yet figured out how to compare the values in two cells or to code a loop.

Answer 1

You can do the following:
Retrieve all contents of column 1 with getRange() and getValues() and push them into an array
Verify with indexOf() either the value in the temporary holding cell matches an entry of the array and if so - retrieve the entry position index
Use setValue() to insert a timestamp into a cell of column 3, row index
Here is a sample:
function myFunction() {
var sheet=SpreadsheetApp.getActiveSpreadsheet().getSheetByName("Sheet1");
var startRow=2;
var lastRow=sheet.getLastRow();
var numberRows=lastRow-startRow+1
var Ids=sheet.getRange(startRow,1,numberRows,1).getValues();
var temporary=sheet.getRange(2,4).getValue();//please modify according to the position of your temporary cell
var array=[];
var timestamp=Utilities.formatDate(new Date(), "GMT", "yyyy-MM-dd'T'HH:mm:ss'Z'");
for(var i=0;i<numberRows;i++){
array.push(Ids[i][0]);
}
var index=array.indexOf(temporary);
if(index!=-1){
sheet.getRange(index+startRow,3).setValue(timestamp);
}
}
You might want to incorporate in a doGet() function of a Web App deployment that will run the code automatically when new data is inserted into the temporary cell.