pxt-calliope/docs/reference/basic/forever.md

Forever

Keep running part of a program in the background.

basic.forever(() => {
})

Example: compass

The following example constantly checks the compass heading and updates the screen with the direction.

let degrees = 0
basic.forever(() => {
    degrees = input.compassHeading()
    if (degrees < 45) {
        basic.showString("N")
    } else if (degrees < 135) {
        basic.showString("E")
    } else if (degrees < 225) {
        basic.showString("S")
    } else if (degrees < 315) {
        basic.showString("W")
    } else {
        basic.showString("N")
    }
})

Example: counter

The following example keeps showing the number stored in a global variable. When you press button A, the number gets bigger. You can use a program like this to count things with your @boardname@.

let num = 0
basic.forever(() => {
    basic.showNumber(num)
})
input.onButtonPressed(Button.A, () => {
    num = num + 1
})

Competing for the LED screen

If different parts of a program are each trying to show something on the LED screen at the same time, you may get unexpected results. Try this on your @boardname@:

basic.forever(() => {
    basic.showNumber(6789)
})
input.onButtonPressed(Button.A, () => {
    basic.showNumber(2)
})

See also

while, on button pressed, in background