now that we're not relying on hoisting outside the NODE_ENV check, convert to let/const. (https://github.com/developit/preact/pull/1525#discussion_r273351184)
now that we're not relying on hoisting outside the NODE_ENV check, convert to let/const. (https://github.com/developit/preact/pull/1525#discussion_r273351184)

technically, `loggedTypeFailures` could also be const depending on project style

developit/preact,developit/preact