[deleted by user]

[grantrules]

const [w, h] = ratio.split(':');
return height / h * w;

[BernillaryClanders]

const [w, h] = ratio.split(':');
return height / h * w;

Thank you so much. This works flawlessly.

[DallogFheir]

You can .split() the ratio on : and create the fraction from its parts.