Optimize compilation events to prevent unneeded stats.toJson() call (#…

…182)

* Optimize compilation events to prevent unneeded stats.toJson() call

* Switch fron nanobus to EventEmitter to fix tests

Per nanobus documentation:
> ### When shouldn't I use this package?
> If you're only writing code that runs inside Node and don't need a '*' listener, consider using the built-in event emitter API instead.

* Remove nanobus dependency

* Revert "Remove nanobus dependency"

This reverts commit 92fca9e.

* Revert "Switch fron nanobus to EventEmitter to fix tests"

This reverts commit 55fef9f.

* Address comments

Some tests are timing out locally, but I can't figure out why. Maybe it's just an issue on my box?

* chore: save result of hasErrors/Warnings, remove event name const

note: the event name object const(s) really weren't needed as the event
names only appear twice each.

index.js

@@ -38,13 +38,23 @@ module.exports = (opts) => {
         });
 
         comp.hooks.done.tap('WebpackServe', (stats) => {
-          const json = stats.toJson();
-          if (stats.hasErrors()) {
-            bus.emit('compiler-error', { json, compiler: comp });
-          }
-
-          if (stats.hasWarnings()) {
-            bus.emit('compiler-warning', { json, compiler: comp });
+          const hasErrors = stats.hasErrors();
+          const hasWarnings = stats.hasWarnings();
+          // stats.toJson() has a high time-cost for large projects
+          // only run that if there are listeners AND there are
+          // problems with the build (#181)
+          if (
+            (bus.listeners('compiler-error').length && hasErrors) ||
+            (bus.listeners('compiler-warning').length && hasWarnings)
+          ) {
+            const json = stats.toJson();
+            if (hasErrors) {
+              bus.emit('compiler-error', { json, compiler: comp });
+            }
+
+            if (hasWarnings) {
+              bus.emit('compiler-warning', { json, compiler: comp });
+            }
           }
 
           bus.emit('build-finished', { stats, compiler: comp });