For more information, read The micro:bit - a reactive system. It is pretty advanced!
Run In Background
Run part of a program while the rest of it is doing something else.
control.inBackground(() => {
})Example
This program shows how running in the background can say what is
stored in a variable like num, while another part (on button pressed)
changes what is stored there.
let num = 0
control.inBackground(() => {
    while (true) {
        basic.showNumber(num)
        basic.pause(100)
    }
})
input.onButtonPressed(Button.A, () => {
    num++;
})This program does the same thing, but in a more usual way,
with a forever loop.
let num = 0
basic.forever(() => {
    basic.showNumber(num)
})
input.onButtonPressed(Button.A, () => {
    num++;
}) 
            