Debounce progress updates

Summary: This shows at max 5 progress updates per second on the terminal, which results in a minor speedup of reloads.

Reviewed By: bestander

Differential Revision: D3620164

fbshipit-source-id: d1a30f2f29f7088602d276b8ad3fc8ff1b74c79d

react-packager/src/Bundler/index.js

@@ -351,14 +351,13 @@ class Bundler {
     if (!resolutionResponse) {
       let onProgress = noop;
       if (process.stdout.isTTY && !this._opts.silent) {
-        const bar = new ProgressBar(
-          'transformed :current/:total (:percent)',
-          {complete: '=', incomplete: ' ', width: 40, total: 1},
-        );
-        onProgress = (_, total) => {
-          bar.total = total;
-          bar.tick();
-        };
+        const bar = new ProgressBar('transformed :current/:total (:percent)', {
+          complete: '=',
+          incomplete: ' ',
+          width: 40,
+          total: 1,
+        });
+        onProgress = debouncedTick(bar);
       }
 
       resolutionResponse = this.getDependencies({
@@ -708,4 +707,23 @@ function getMainModule({dependencies, numPrependedDependencies = 0}) {
   return dependencies[numPrependedDependencies];
 }
 
+function debouncedTick(progressBar) {
+  let n = 0;
+  let start, total;
+
+  return (_, t) => {
+    total = t;
+    n += 1;
+    if (start) {
+      if (progressBar.curr + n >= total || Date.now() - start > 200) {
+        progressBar.total = total;
+        progressBar.tick(n);
+        start = n = 0;
+      }
+    } else {
+      start = Date.now();
+    }
+  };
+}
+
 module.exports = Bundler;