It is possible to watch expression and variable values while debugging. On every breakpoint, each expression from the watchers list will be evaluated in the current context and displayed immediately before the breakpoint's source code listing.
An alternative method that I have found to be effective in lieu of a watch facility is adding a conditional breakpoint using
M-x indium-add-conditional-breakpoint and using a
console.log(...) expression. Since that always returns undefined, it will print to the
*JS REPL* buffer whenever passing that line of code.
The behavior is less than ideal since it is different than a watch statement (i.e. multiple watch statements are not printed simultaneously).