It would be nice if V8 Extras could use a v8.ASSERT() function which would work in debug builds but be compiled out of optimised builds. Or it could just be a no-op in optimised builds, which would still be useful for many cheap checks.

I am thinking of a syntax like

v8.ASSERT(condition, message)

which would do nothing if |condition| was true. If |condition| was false, it would print
`Assertion failed: ${message}`, then a stack trace, and abort hard enough to cause a layout test to fail (crashing the process would fulfill this requirement).

Example:

v8.ASSERT(new Date() > 0, 'Javascript has been invented');