Add ability for wait function to take a callback

README.md

@@ -55,9 +55,10 @@ Throw an error if it does not.
 The expectation can be a string (the line should contain the expected value as
 a substring) or a RegExp (the line should match the expression).
 
-### function wait (expectation)
+### function wait (expectation, callback)
 
 * expectation {string|RegExp} Output to assert on the target stream
+* callback {Function} **Optional** Callback to be called when output matches stream
 
 Wait for a line of output that matches the expectation, discarding lines
 that do not match.
@@ -67,6 +68,8 @@ Throw an error if no such line was found.
 The expectation can be a string (the line should contain the expected value as
 a substring) or a RegExp (the line should match the expression).
 
+The callback will be called for every line that matches the expectation.
+
 ### function sendline (line)
 
 * line {string} Output to write to the child process.

lib/nexpect.js

@@ -24,9 +24,13 @@ function chain (context) {
 
       return chain(context);
     },
-    wait: function (expectation) {
+    wait: function (expectation, callback) {
       var _wait = function _wait (data) {
-        return testExpectation(data, expectation);
+        var val = testExpectation(data, expectation);
+        if (val === true && typeof callback === 'function') {
+          callback(data);
+        }
+        return val;
       };
 
       _wait.shift = false;

test/nexpect-test.js

@@ -85,7 +85,40 @@ vows.describe('nexpect').addBatch({
                  .wait('second')
                  .sendline('second-prompt')
                  .wait('this-never-shows-up')
-        )
+        ),
+        "when a callback is provided and output is matched": {
+          topic: function() {
+            var expect = nexpect.spawn(path.join(__dirname, 'fixtures', 'prompt-and-respond'))
+              .wait('first', this.callback)
+              .sendline('first-prompt')
+              .expect('first-prompt')
+              .wait('second')
+              .sendline('second-prompt')
+              .expect('second-prompt').run(function() {});
+          },
+          'should call callback': function(matchData, b) {
+            assert.ok(matchData.indexOf('first') > 0, "Found 'first' in output")
+          }
+        },
+        "when a callback is provided and output is not matched": {
+          topic: function() {
+            var args = {hasRunCallback: false},
+                waitCallback = function() {
+                  args.hasRunCallback = true;
+                };
+
+            var expect = nexpect.spawn(path.join(__dirname, 'fixtures', 'prompt-and-respond'))
+              .wait('first')
+              .sendline('first-prompt')
+              .expect('first-prompt')
+              .wait('second')
+              .sendline('second-prompt')
+              .wait('this-never-shows-up', waitCallback).run(this.callback.bind(this, args));
+          },
+          'should not call callback': function(args, a) {
+            assert.equal(args.hasRunCallback, false, 'Should not have run callback');
+          }
+        }
       },
       "when options.stripColors is set": assertSpawn(
         nexpect.spawn(path.join(__dirname, 'fixtures', 'log-colors'), { stripColors: true })