Use let instead of var throughout. All modern browsers support it and have for many years, even the now-EOL IE11.[^ie]
Add a @ts-check annotation so that anyone working on a TS-enabled editor will get feedback inline about cases they may otherwise miss.
Add JSDoc-based type definitions for the script, and fix some errors that may occur at runtime. (These will be rare if they happen, but getting rid of them is still a win!)
screenshots to show it still works
[^ie]: IE11 did not correctly support the semantics of let for for loops, but the uses in the existing code here already used var in a way which would trigger the same behavior as using let does.
letinstead ofvarthroughout. All modern browsers support it and have for many years, even the now-EOL IE11.[^ie]@ts-checkannotation so that anyone working on a TS-enabled editor will get feedback inline about cases they may otherwise miss.screenshots to show it still works
 [^ie]: IE11 did not correctly support the semantics of
letforforloops, but the uses in the existing code here already usedvarin a way which would trigger the same behavior as usingletdoes.