introduce debug.id helper method

src/common.js

@@ -65,6 +65,7 @@ module.exports = function setup(env) {
 
   function createDebug(namespace) {
     var prevTime;
+    var lastId = 0;
 
     function debug() {
       // disabled?
@@ -118,11 +119,19 @@ module.exports = function setup(env) {
       logFn.apply(self, args);
     }
 
+    function id () {
+      // disabled?
+      if (!debug.enabled) return;
+
+      return lastId++;
+    }
+
     debug.namespace = namespace;
     debug.enabled = createDebug.enabled(namespace);
     debug.useColors = createDebug.useColors();
     debug.color = selectColor(namespace);
     debug.destroy = destroy;
+    debug.id = id;
     //debug.formatArgs = formatArgs;
     //debug.rawLog = rawLog;
 

test/debug_spec.js

@@ -62,6 +62,21 @@ describe('debug', function () {
         expect(log.log).to.have.been.calledOnce;
       });
     });
+
+    context('with `log.id` function', function () {
+      it('increments internal id when enabled', function () {
+        expect(log.id()).to.equal(0);
+        expect(log.id()).to.equal(1);
+        expect(log.id()).to.equal(2);
+      });
+
+      it('does not increment internal id when disabled', function () {
+        debug.disable('test');
+
+        expect(log.id()).to.equal(undefined);
+        expect(log.id()).to.equal(undefined);
+      });
+    });
   });
 
 });