angular : $eval & $timeout

$digest: function() {
        var watch, value, last,
            watchers,
            length,
            dirty, ttl = TTL,
            next, current, target = this,
            watchLog = [],
            logIdx, logMsg, asyncTask;

        beginPhase('$digest');
        // Check for changes to browser url that happened in sync before the call to $digest
        $browser.$$checkUrlChange();

        if (this === $rootScope && applyAsyncId !== null) {
          // If this is the root scope, and $applyAsync has scheduled a deferred $apply(), then
          // cancel the scheduled $apply and flush the queue of expressions to be evaluated.
          $browser.defer.cancel(applyAsyncId);
          flushApplyAsync();
        }

        lastDirtyWatch = null;

        do { // "while dirty" loop
          dirty = false;
          current = target;

          while (asyncQueue.length) { //先跑$eval
            try {
              asyncTask = asyncQueue.shift();
              asyncTask.scope.$eval(asyncTask.expression, asyncTask.locals);
            } catch (e) {
              $exceptionHandler(e);
            }
            lastDirtyWatch = null;
          }

          traverseScopesLoop:
          do { // "traverse the scopes" loop
            if ((watchers = current.$$watchers)) {
              // process our watches
              length = watchers.length;
              while (length--) {
                try {
                  watch = watchers[length];
                  // Most common watches are on primitives, in which case we can short
                  // circuit it with === operator, only when === fails do we use .equals
                  if (watch) {
                    if ((value = watch.get(current)) !== (last = watch.last) &&
                        !(watch.eq
                            ? equals(value, last)
                            : (typeof value === 'number' && typeof last === 'number'
                               && isNaN(value) && isNaN(last)))) {
                      dirty = true;
                      lastDirtyWatch = watch;
                      watch.last = watch.eq ? copy(value, null) : value;
                      watch.fn(value, ((last === initWatchVal) ? value : last), current);
                      if (ttl < 5) {
                        logIdx = 4 - ttl;
                        if (!watchLog[logIdx]) watchLog[logIdx] = [];
                        watchLog[logIdx].push({
                          msg: isFunction(watch.exp) ? 'fn: ' + (watch.exp.name || watch.exp.toString()) : watch.exp,
                          newVal: value,
                          oldVal: last
                        });
                      }
                    } else if (watch === lastDirtyWatch) {
                      // If the most recently dirty watcher is now clean, short circuit since the remaining watchers
                      // have already been tested.
                      dirty = false;
                      break traverseScopesLoop;
                    }
                  }
                } catch (e) {
                  $exceptionHandler(e);
                }
              }
            }

            // Insanity Warning: scope depth-first traversal
            // yes, this code is a bit crazy, but it works and we have tests to prove it!
            // this piece should be kept in sync with the traversal in $broadcast
            if (!(next = ((current.$$watchersCount && current.$$childHead) ||
                (current !== target && current.$$nextSibling)))) {
              while (current !== target && !(next = current.$$nextSibling)) {
                current = current.$parent;
              }
            }
          } while ((current = next));

          // `break traverseScopesLoop;` takes us to here

          if ((dirty || asyncQueue.length) && !(ttl--)) {
            clearPhase();
            throw $rootScopeMinErr('infdig',
                '{0} $digest() iterations reached. Aborting!\n' +
                'Watchers fired in the last 5 iterations: {1}',
                TTL, watchLog);
          }

        } while (dirty || asyncQueue.length);

        clearPhase();

        while (postDigestQueue.length) {//最后跑$timeout
          try {
            postDigestQueue.shift()();
          } catch (e) {
            $exceptionHandler(e);
          }
        }
      },

angular digest 会先跑 $browser.$$checkUrlChange();， 其他的我带过，接着就是check dirty 和 asyncQueue.length。 最后是check postDigestQuese.length