What I like in the old codebase of web projects. it's chance to see history of real projects in old "dark" times of web. For example you take a look on the line code of project with 10 years history:

scaleZoom = Math.log(scale) / Math.LN2;

And you remember school course of algebra with properties of logarithms like ${\log }_{a}b=\frac{{\log }_{c}b}{{\log }_{c}a}$ and also remember that support of Math.log2 in browsers was added a little bit later than Math.log and developers with math in mind used to made this trick.