Few banner ad example

const banner = [ '<a href="http://some.url" target="_blank"><img src="some.jpg"></a>',
            '<a href="http://some.url" target="_blank"><img src="some.jpg"></a>',
            '<a href="http://some.url" target="_blank"><img src="some.jpg"></a>',
            '<a href="http://some.url" target="_blank"><img src="some.jpg"></a>',
            '<a href="http://some.url" target="_blank"><img src="some.jpg"></a>'
]

const getRandomNumber = (min, max) => Math.floor(Math.random() * (max - min) + min)

const getNumber = getRandomNumber(banner.length, 1)

document.write(banner[getNumber])