Scripter Javascript Tutorial

61 The if...else statement

MDN: Control Flow and Error Handling: if...else statement

The if...else statement accommodates handling code to execute when a condition is either true or false. The syntax is very similar:

if ( <condition is true> ) {
	<do something>
} else {
	<do something else>
}

In the above example:

• Lines 1–2: These are exactly the same as the if statement.

• Line 3: The first curly brace closes the true code block and the false code block is opened with the else keyword and the curly brace.

• Line 4: The code to be executed when the condition is false.

• Line 5: The false code block, and the entire if...else statement, is closed with the curly brace.

To expand upon the example in HandleMIDI(), because there are many types of events:

function HandleMIDI(event) {
	if (event instanceof NoteOn) {
		Trace("NoteOn");
	} else {
		Trace(event);
	}
}

In the above example, the following is happening:

• Line 1: Scripter calls the HandleMIDI() function, passing an event.

• Line 2: The if statement evaluates whether the event is an instance of NoteOn.

• Line 3: If the event is NoteOn, then the event is written to the console.

• Line 4: The if statement is closed with the curly brace.

For a simple track with one note, the following is output to the console:

***Creating a new MIDI engine with script***

Evaluating MIDI-processing script...
Script evaluated successfully!
NoteOn
[NoteOff channel:1 pitch:61 [C#3] velocity:64]
[ControlChange channel:1 number:120 [All Sound Off] value:0]
>

In the output, note the following:

• Line 5: The NoteOn event is captured per the condition event instanceof NoteOn and all that is output is the string “NoteOn”.

• Lines 6–7: Neither event is a NoteOn, so the script outputs the events themselves to the console.