added first A/B experiment

app/experiments.js

@@ -0,0 +1,76 @@
+import hash from 'string-hash';
+
+const experiments = {
+  '5YHCzn2CQTmBwWwTmZupBA': {
+    id: '5YHCzn2CQTmBwWwTmZupBA',
+    run: function(variant, state, emitter) {
+      state.experiment = {
+        xid: this.id,
+        xvar: variant
+      };
+      // Beefy UI
+      if (variant === 1) {
+        state.config.uploadWindowStyle = 'upload-window upload-window-b';
+        state.config.uploadButtonStyle = 'btn browse browse-b';
+      } else {
+        state.config.uploadWindowStyle = 'upload-window';
+        state.config.uploadButtonStyle = 'btn browse';
+      }
+      emitter.emit('render');
+    },
+    eligible: function(state) {
+      return this.luckyNumber(state) >= 0.5;
+    },
+    variant: function(state) {
+      return this.luckyNumber(state) < 0.5 ? 0 : 1;
+    },
+    luckyNumber: function(state) {
+      return luckyNumber(
+        `${this.id}:${state.storage.get('testpilot_ga__cid')}`
+      );
+    }
+  }
+};
+
+//Returns a number between 0 and 1
+function luckyNumber(str) {
+  return hash(str) / 0xffffffff;
+}
+
+function checkExperiments(state, emitter) {
+  const all = Object.keys(experiments);
+  const id = all.find(id => experiments[id].eligible(state));
+  if (id) {
+    const variant = experiments[id].variant(state);
+    state.storage.enroll(id, variant);
+    experiments[id].run(variant, state, emitter);
+  }
+}
+
+export default function initialize(state, emitter) {
+  emitter.on('DOMContentLoaded', () => {
+    const xp = experiments[state.query.x];
+    if (xp) {
+      xp.run(state.query.v, state, emitter);
+    }
+  });
+
+  if (!state.storage.get('testpilot_ga__cid')) {
+    // first ever visit. check again after cid is assigned.
+    emitter.on('DOMContentLoaded', () => {
+      checkExperiments(state, emitter);
+    });
+  } else {
+    const enrolled = state.storage.enrolled;
+    enrolled.forEach(([id, variant]) => {
+      const xp = experiments[id];
+      if (xp) {
+        xp.run(variant, state, emitter);
+      }
+    });
+    // single experiment per session for now
+    if (enrolled.length === 0) {
+      checkExperiments(state, emitter);
+    }
+  }
+}