1 files changed, 54 insertions, 8 deletions

diff --git a/app/scripts/lib/migrator/index.js b/app/scripts/lib/migrator/index.js
index 4fd2cae92..345ca8001 100644
--- a/app/scripts/lib/migrator/index.js
+++ b/app/scripts/lib/migrator/index.js
@@ -1,6 +1,25 @@
-class Migrator {
+const EventEmitter = require('events')
 
+/**
+ * @typedef {object} Migration
+ * @property {number} version - The migration version
+ * @property {Function} migrate - Returns a promise of the migrated data
+ */
+
+/**
+ * @typedef {object} MigratorOptions
+ * @property {Array<Migration>} [migrations] - The list of migrations to apply
+ * @property {number} [defaultVersion] - The version to use in the initial state
+ */
+
+class Migrator extends EventEmitter {
+
+  /**
+   * @constructor
+   * @param {MigratorOptions} opts
+   */
   constructor (opts = {}) {
+    super()
     const migrations = opts.migrations || []
     // sort migrations by version
     this.migrations = migrations.sort((a, b) => a.version - b.version)
@@ -12,30 +31,57 @@ class Migrator {
 
   // run all pending migrations on meta in place
   async migrateData (versionedData = this.generateInitialState()) {
+    // get all migrations that have not yet been run
     const pendingMigrations = this.migrations.filter(migrationIsPending)
 
+    // perform each migration
     for (const index in pendingMigrations) {
       const migration = pendingMigrations[index]
-      versionedData = await migration.migrate(versionedData)
-      if (!versionedData.data) throw new Error('Migrator - migration returned empty data')
-      if (versionedData.version !== undefined && versionedData.meta.version !== migration.version) throw new Error('Migrator - Migration did not update version number correctly')
+      try {
+        // attempt migration and validate
+        const migratedData = await migration.migrate(versionedData)
+        if (!migratedData.data) throw new Error('Migrator - migration returned empty data')
+        if (migratedData.version !== undefined && migratedData.meta.version !== migration.version) throw new Error('Migrator - Migration did not update version number correctly')
+        // accept the migration as good
+        versionedData = migratedData
+      } catch (err) {
+        // rewrite error message to add context without clobbering stack
+        const originalErrorMessage = err.message
+        err.message = `MetaMask Migration Error #${migration.version}: ${originalErrorMessage}`
+        console.warn(err.stack)
+        // emit error instead of throw so as to not break the run (gracefully fail)
+        this.emit('error', err)
+        // stop migrating and use state as is
+        return versionedData
+      }
     }
 
     return versionedData
 
-    // migration is "pending" if it has a higher
-    // version number than currentVersion
+    /**
+     * Returns whether or not the migration is pending
+     *
+     * A migration is considered "pending" if it has a higher
+     * version number than the current version.
+     * @param {Migration} migration
+     * @returns {boolean}
+     */
     function migrationIsPending (migration) {
       return migration.version > versionedData.meta.version
     }
   }
 
-  generateInitialState (initState) {
+  /**
+   * Returns the initial state for the migrator
+   * @param {object} [data] - The data for the initial state
+   * @returns {{meta: {version: number}, data: any}}
+   */
+  generateInitialState (data) {
     return {
       meta: {
         version: this.defaultVersion,
       },
-      data: initState,
+      data,
     }
   }