micro:bit light looping

light_loop.js

let pos = 0
let colour = 0
let len = 0
let stretch = 0
let item: neopixel.Strip = null
let LED_Count = 0
LED_Count = 90
item = neopixel.create(DigitalPin.P0, LED_Count, NeoPixelMode.RGB)
item.clear()
item.easeBrightness()
stretch = 15
len = LED_Count - stretch
basic.forever(() => {
    item.clear()
    for (let index = 0; index <= LED_Count + stretch / 1; index++) {
        if (index >= LED_Count) {
            index = index - LED_Count
        }
        item.show()
        for (let list = 0; list <= stretch / 2; list++) {
            colour = neopixel.rgb(255 - list / 2, 10 * (list / 2), 30 * (list * 2))
            item.setPixelColor(index - list, colour)
        }
        colour = neopixel.rgb(255, 30, 15)
        item.setPixelColor(index, colour)
        item.setPixelColor(index + 1, colour)
        item.setPixelColor(index - 1, colour)
        item.setPixelColor(index + (stretch + 1), neopixel.rgb(0, 0, 0))
        pos = index - (stretch + 1)
        if (0 > pos) {
            pos = pos + LED_Count
        }
        item.setPixelColor(pos, neopixel.rgb(0, 0, 0))
        item.show()
        if (index <= 30) {
            basic.pause(20)
        }
        basic.pause(20)
    }
})