Morse Code Pager for BBC Micro:Bit

/* This is a piece of code my friend and I wrote for the Micro:Bit which turns it into a Morse-Code-based pager.
   Button A sends '.', Button B sends '-', and pressing the two together sends a space.
   The Micro:Bit can then be shaken to send the character. */

enum RadioMessage {
    message1 = 49434
}

input.onButtonPressed(Button.A, function () {
    CharacterToDecode = "" + CharacterToDecode + "."
})

input.onButtonPressed(Button.B, function () {
    CharacterToDecode = "" + CharacterToDecode + "-"
})

input.onButtonPressed(Button.AB, function () {
    radio.sendString(" ")
    CharacterToDecode = ""
})

radio.onReceivedString(function (receivedString) {
    basic.clearScreen()
    basic.showString(receivedString)
})

input.onGesture(Gesture.Shake, function () {
    if (!(CharacterToDecode.isEmpty())) {
        radio.sendString("" + (alphabet[morse.indexOf(CharacterToDecode)]))
        CharacterToDecode = ""
    }
    CharacterToDecode = ""
})

let alphabet: string[] = []
let morse: string[] = []
let CharacterToDecode = ""
radio.setTransmitPower(7)
radio.setFrequencyBand(1)
CharacterToDecode = ""

morse = [
".-",
"-...",
"-.-.",
"-..",
".",
"..-.",
"--.",
"....",
"..",
".---",
"-.-",
".-..",
"--",
"-.",
"---",
".--.",
"--.-",
".-.",
"...",
"-",
"..-",
"...-",
".--",
"-..-",
"-.--",
"--..",
".----",
"..---",
"...--",
"....-",
".....",
"-....",
"--...",
"---..",
"----.",
"-----"
]
alphabet = [
"A",
"B",
"C",
"D",
"E",
"F",
"G",
"H",
"I",
"J",
"K",
"L",
"M",
"N",
"O",
"P",
"Q",
"R",
"S",
"T",
"U",
"V",
"W",
"X",
"Y",
"Z",
"1",
"2",
"3",
"4",
"5",
"6",
"7",
"8",
"9",
"0"
]