Accept generator function for error message

[davidje13]

For dev-time error messages (and for those not using build-time rewriters), it would be nice if time-consuming calculations for error messages were only performed in the event of an error. This would be easy to achieve with minimal bloat using a lambda:

invariant(something, () => `my message with ${complex()} calculations`)

The build-time rewriters will be able to strip this with no changes necessary.

Internally:

throw new Error(`${prefix}: ${typeof message == 'function' ? message() : message || ''}`);

[alexreardon]

🤔

[alexreardon]

How does this look @davidje13? https://github.com/alexreardon/tiny-invariant/pull/76/files

[alexreardon]

Closed by mistake

[alexreardon]

Now released https://github.com/alexreardon/tiny-invariant/releases/tag/v1.2.0