As I've answered in another question, the function is often written in Script Include instead of with the script creating ScheduleOnce).

So something like below. 

Script Include:

var ScheduledJobExample = Class.create();
ScheduledJobExample.prototype = {
    initialize: function() {},
    output2log: function(argument) {
        gs.info(argument);
    },
    type: 'ScheduledJobExample'
};

Schedule script:

var argument ="Test OK";
var sched = new ScheduleOnce();
sched.script = "var si = new ScheduledJobExample().output2log('" + argument + "');";
sched.schedule();

Here, sched.script is create a script include class ScheduledJobExample and calls function named "output2log()" with argument defined by variable "argument".

That is, sched.script is just a string with javascript script to execute in the job.

thank you for answering.
The code for "Schedule Once" is as follows:

   schedule: function() {
      var t = this._getTrigger();
      
      // calc and set time
      var n = parseInt(this.seconds);
      n += parseInt(this.minutes) * 60;
      n += parseInt(this.hours) * 60 * 60;
      n += parseInt(this.days) * 24 * 60 * 60;
      this.time.addSeconds(n);
      t.next_action.setValue( this.time );
      
      t.trigger_type = this.trigger_type;
      gs.print("Scheduling: " + this.label + " for: " + t.next_action.getDisplayValue());
      return t.insert();
   },

var t = this._getTrigger();

In the above code, it seems that the following code of the contents of "Schedule" of the script include is called.

  // call after variables are setup
  _getTrigger: function() {
     var t = new GlideRecord('sys_trigger');
     t.initialize();
     t.name = this.label; 
     t.document = this.document;
     t.document_key = this.document_key;
     t.script = this.script;
     t.job_id = this.job_id;
     if (!gs.nil(this.system_id))
       t.system_id = this.system_id;
     return t;
  },

I found that the above code created a new record in the "sys_trigger" table.

Does "sched.script =" when using "Schedule Once" mean to set the script in the yellow marker part of the image below?

Do you know where to check the results of the schedule you ran?

Thank you!
I deepened my understanding!

Hi Hitoshi, 

I am trying to schedule a function that belongs to the same class using your method, but It does not seem to work. 

var scheduleTest = Class.create();
scheduleTest .prototype = {
    initialize: function(addButton) {
		gs.debug("User in initialize funciton: " + gs.getUser());
		this.addButton = addButton
    },
	debugLog: function(){
		gs.debug("Schedule executed");
	},
	
	mySchedule: function(){
        gs.debug("scheduleTest reached");
		var argument ="Schedule test";
		var gdt = new GlideDateTime();
		gdt.addSeconds(1);
		var sched = new global.ScheduleOnce();
		sched.script = '('+debugLog+')("'+argument+'");';
		sched.setTime(gdt);
		sched.setLabel("run this as system");
		sched.schedule();
	},

    type: 'scheduleTest '
};

scheduleTest() is called from another script include. scheduleTest() executes fine (I can see the debug message in Session Logs) but it does not call schedTest(). I am not sure what I'm doing wrong here. Any help would be appreciated. 

Thanks, 

T.