Class FormTriggerBuilder

var form = FormApp.openById('1234567890abcdefghijklmnopqrstuvwxyz');
ScriptApp.newTrigger('myFunction')
    .forForm(form)
    .onFormSubmit()
    .create();

var form = FormApp.getActiveForm();
ScriptApp.newTrigger('myFunction')
    .forForm(form)
    .onOpen()
    .create();