* generateAppId should take param in favor of local state

* add hint to generatePublicKey method about callback parameter

src/crx.js

@@ -129,8 +129,9 @@ ChromeExtension.prototype = {
    * Generates a public key.
    *
    * BC BREAK `this.publicKey` is not stored anymore (since 1.0.0)
+   * BC BREAK callback parameter has been removed in favor to the promise interface.
    *
-   * @returns {Promise}
+   * @returns {Promise} Resolves to {Buffer} containing the public key
    * @example
    *
    * crx.generatePublicKey(function(publicKey){
@@ -261,16 +262,19 @@ ChromeExtension.prototype = {
    * Public key has to be set for this to work, otherwise an error is thrown.
    *
    * BC BREAK `this.appId` is not stored anymore (since 1.0.0)
+   * BC BREAK introduced `publicKey` parameter as it is not stored any more since 2.0.0
    *
+   * @param {Buffer|string} [publicKey] the public key to use to generate the app ID
    * @returns {string}
    */
-  generateAppId: function () {
-    if (typeof this.publicKey !== 'string' && !(this.publicKey instanceof Buffer)) {
-      throw new Error('Public key is not set');
+  generateAppId: function (publicKey) {
+    publicKey = publicKey || this.publicKey;
+    if (typeof publicKey !== 'string' && !(publicKey instanceof Buffer)) {
+      throw new Error('Public key is neither set, nor given');
     }
     return crypto
       .createHash("sha256")
-      .update(this.publicKey)
+      .update(publicKey)
       .digest("hex")
       .slice(0, 32)
       .replace(/./g, function (x) {

test/index.js

@@ -66,5 +66,5 @@ test('it should fail if the extension content is loaded without having prelimina
 test('it should fail if the public key was not set prior to trying to generate the app ID', function(t) {
   t.plan(1);
   var crx = newCrx();
-  t.throws(function() { crx.generateAppId(); }, /Public key is not set/);
+  t.throws(function() { crx.generateAppId(); }, /Public key is neither set, nor given/);
 });