I should think well suited to Espruino ... Micro:Bit v2 countdown timer, with announcement

I think what you need is similar to the example on https://www.espruino.com/MicroBit#micro-bit-functionality. Something like this should work

g = Graphics.createArrayBuffer(5,5,1);
g.flip = function(){show(this.buffer);};

function countdown() {
  x--;
  g.clear();  
  if (x<=0) { // finished
    clearInterval(intr);
    intr = undefined;
    g.fillRect(0,0,5,5);
    // long beep
    analogWrite(Microbit.SPEAKER,0.5, {freq:2500});
    setTimeout(() => Microbit.SPEAKER.reset(), 500);
  } else { // count down
    g.drawString(x);
    // beep
    analogWrite(Microbit.SPEAKER,0.5, {freq:3000});
    setTimeout(() => Microbit.SPEAKER.reset(), 100);
  }
  g.flip();  
}

var x = 10;
countdown();
var intr = setInterval(countdown, 1000);