Making a "gif" with JavaScript

I would like to create a gif-type animation if the distance between me and the person ahead/behind increses/decreses. Since SimHUB doesn't support gif I was woundering if this could be done with JS?

Something like this:

var gapAhead = $prop('IRacingExtraProperties.iRacing_NonRelativeDriverAheadInClass_00_GapChangeLastLap')

if (gapAhead >= 0) {
    return 'The JS-script would go here'
}

else {
   return 'Same JS-script, but with other images'
}