isEligible should fire on route change

lib/plugin.js

@@ -5,14 +5,23 @@ import experiments from '<%= options.experimentsDir %>'
 const MAX_AGE = <%= options.maxAge %>
 
 export default function (ctx, inject) {
+  ctx.app.router.beforeEach((to, from, next) => {
+    trackExperiment(ctx);
+    next();
+  });
+
+  trackExperiment(ctx);
+
+  // Inject $exp
+  inject('exp', ctx.experiment)
+}
+
+function trackExperiment(ctx) {
   // Assign experiment and variant to user
   assignExperiment(ctx)
 
   // Google optimize integration
   googleOptimize(ctx)
-
-  // Inject $exp
-  inject('exp', ctx.experiment)
 }
 
 function assignExperiment(ctx) {
@@ -27,25 +36,29 @@ function assignExperiment(ctx) {
   const [cookieExp, cookieVars] = cookie.split('.')
   if (cookieExp.length) {
     // Try to find experiment with that id
-    experimentIndex = experiments.findIndex(exp => exp.experimentID === cookie[0])
+    experimentIndex = experiments.findIndex(exp => exp.experimentID === cookieExp)
 
     // Variant indexes
     variantIndexes = cookieVars.split('-').map(v => parseInt(v))
   }
 
   // Choose one experiment
-  const experimentWeights = experiments.map(exp => exp.weight === undefined ? 1 : exp.weight)
-  let retries = experiments.length
-  while (experimentIndex === -1 && retries-- > 0) {
-    experimentIndex = weightedRandom(experimentWeights)
+  if (experimentIndex !== -1) {
     experiment = experiments[experimentIndex]
-
-    // Check if current user is eligible for experiment
-    if (typeof experiment.isEligible === 'function') {
-      if (!experiment.isEligible(ctx)) {
-        // Try another one
-        experimentWeights[experimentIndex] = 0
-        experimentIndex = -1
+  } else {
+    const experimentWeights = experiments.map(exp => exp.weight === undefined ? 1 : exp.weight)
+    let retries = experiments.length
+    while (experimentIndex === -1 && retries-- > 0) {
+      experimentIndex = weightedRandom(experimentWeights)
+      experiment = experiments[experimentIndex]
+
+      // Check if current user is eligible for experiment
+      if (typeof experiment.isEligible === 'function') {
+        if (!experiment.isEligible(ctx)) {
+          // Try another one
+          experimentWeights[experimentIndex] = 0
+          experimentIndex = -1
+        }
       }
     }
   }