Unit 3 · Module 2

Triggers

Simple triggers, installable triggers, and the editor UI where they get configured

Why this page exists

Module 1 named “trigger” as one of the four parts of a script. This is the page where Apps Script’s specific trigger system gets pinned down. Without a trigger, a script just sits in the editor doing nothing.

The two kinds of triggers

	Simple triggers	Installable triggers
How they’re set up	Just by naming the function a special reserved name	Configured in the editor UI (Triggers panel)
Function names	`onOpen`, `onEdit`, `onSelectionChange`, `doGet`, `doPost`	Any name the developer picks
What can trigger them	Only user-driven events in the bound document	Time-based, form submit, calendar events, etc. — anything Google supports
Permissions	Limited — can’t call services that require authorization (no sending email as the user, etc.)	Full — runs with the same permissions the developer authorized
Visible in code	Yes (the function exists with the magic name)	No — the trigger lives in the project settings, not the code

Simple triggers, in code

A simple trigger is just a function with a reserved name. Apps Script sees the name and wires the trigger up automatically.

Apps Script — bound to a Sheet

function onOpen() {
  SpreadsheetApp.getUi().alert("Welcome back");
}

function onEdit(e) {
  const editedCell = e.range;
  editedCell.setBackground("#ffeecc");
}

onOpen runs every time the user opens the Sheet. onEdit runs every time the user edits a cell. The developer never writes “listen for opens.” The name is the contract.

The reserved names worth knowing

Function name	Fires when
`onOpen(e)`	User opens a Sheet, Doc, Form, or Slides bound to the script
`onEdit(e)`	User edits a cell in the bound Sheet
`onSelectionChange(e)`	User selects a different cell in the bound Sheet
`onInstall(e)`	User installs the script as an add-on
`doGet(e)` / `doPost(e)`	Script is deployed as a web app and receives an HTTP request (the standard way a browser or another app asks a server for something — covered in Unit 4)

Installable triggers, in the UI

Installable triggers don’t appear in the code. They live in the Apps Script editor under Triggers (the clock icon in the sidebar). Each trigger is a row that says “run this function when this event happens.”

The event options Google offers:

Time-driven. Every minute / hour / day / week / month / at a specific time
From spreadsheet. On open / on edit / on change / on form submit
From form. On open / on form submit
From calendar. Calendar event updated
From document. On open

The function the trigger calls is just a regular function in the script. It can have any name. The trigger is the configuration that wires “event X” to “function Y.”

Apps Script — function called by a daily installable trigger

function sendMorningSummary() {
  const ss = SpreadsheetApp.openById("abc123");
  const sheet = ss.getSheetByName("Orders");
  const count = sheet.getLastRow() - 1;

  GmailApp.sendEmail(
    "me@example.com",
    "Daily summary",
    `Orders today: ${count}`
  );
}

Nothing in this function says “run me daily.” That part lives in the Triggers panel — a row that says “run sendMorningSummary, time-driven, day timer, 7am–8am.”

The connection back to Module 1’s four parts

Simple triggers and installable triggers are both ways of filling in the fourth part of the anatomy from Module 1 — “what causes the entry point to run.” Apps Script just offers two flavors: one configured by function name, one configured in the UI.