Scripter Javascript Tutorial

67 Looping Through Arrays

In the following example, an array is used to store which notes are currently being played in the track. A loop is used to remove notes as NoteOff events are captured. Like the larger example from before, this gets into a function—HandleMIDI()—to provide context for what is happening within the loop itself and the example is a fairly common task when working in Scripter. The actual loop is in lines 10–16:

var activeNotes = [];

function HandleMIDI(event) {

	if ( event instanceof NoteOn ) {
		activeNotes.push(event);
		
	} else if ( event instanceof NoteOff ) {
		var length = activeNotes.length;
		for ( var thisNote = 0; thisNote < length; thisNote++ ) {
			var note = activeNotes[thisNote];
			if ( note.pitch == event.pitch ) {
				activeNotes.splice( thisNote, 1 );
				break;
			}
		}
	}
	
	Trace( activeNotes.length );
}

In the above example:

• Line 1: An array is declared which will store the events. This is created as soon as the "Run Script" button is clicked.

• Line 3: Scripter executes the HandleMIDI() function whenever a new event is encountered.

• Line 5–17: An if...else if statement is used to test what kind of event is being passed into the HandleMIDI() function.

• Lines 5-6: If the event is a NoteOn event, then add it to the activeNotes array.

• Line 8: If the event is a NoteOff event, then the following happens:

  • Line 9: The length of the activeNotes array is captured in the length variable.

  • Line 10: The for statement is declared.

    • var thisNote = 0 declares the loop’s variable. This value will be used as the index to get notes from the activeNotes array. Remember that array indexes begin with 0 and increment by 1 until the last item in the array, which has an index of length - 1.

    • thisNote < activeNotes.length is the condition which is tested. When the index is less than the length of the array, then the code block is executed. When the index equals the length of the array, the loop is immediately stopped and the code block is not executed.

    • thisNote++ will add 1 to the thisNote value after the code block has been executed. Any number can be added to the value for different kinds of increments. For example, to look at every other note in the array, thisNote += 2 would be used.

• Line 11: The current value of thisNote is used as an index in the activeNotes array.

• Lines 12–14: The pitch value for thisNote is compared to the event. If the patches match, then remove the note from activeNotes and stop the loop.