scope - Infinite loop when calling $evalAsync within a $watch function (AngularJS) -

i'm following along tero parviainen's book "build own angularjs" , i'm finding trouble understanding 1 of concepts introduces when talking $evalasync.

in 1 of examples declares watcher calls $evalasync:

it('eventually halts $evalasyncs added watches', function() {   scope.avalue = [1, 2, 3];   scope.$watch(     function(scope) {       scope.$evalasync(function(scope) { });       return scope.avalue;     },     function(newvalue, oldvalue, scope) { }   );   expect(function() { scope.$digest(); }).tothrow(); }); 

seeing example, expect digest cycle iterate twice through watchers until stopping. in implementation of scope, code runs until digest not dirty or there no more $evalasyncs in queue.

scope.prototype.$digest = function () {   var ttl = 10;   var dirty;   this.$$lastdirtywatch = null;   {     while (this.$$asyncqueue.length) {       var asynctask = this.$$asyncqueue.shift();       asynctask.scope.$eval(asynctask.expression);     }     dirty = this.$$digestonce();     if ((dirty || this.$$asyncqueue.length) && !(ttl--)) {       throw '10 digest iterations reached';     }   } while (dirty || this.$$asyncqueue.length); };  

if each iteration in loop, 1 asynctask if shifted array, how comes that loop runs forever? shouldn't loop stop because $$asyncqueue gets emptied?

hope made myself clear , everyone!

by calling:

scope.$evalasync(function(scope) { }); 

you add new item asyncqueue:

asyncqueue.push({scope: this, expression: expr, locals: locals}); 

so removing task this.$$asyncqueue.shift(); call new iteration a.e. new digest cycle.

anyways proper implementation of watcher is:

scope.avalue = [1, 2, 3];   scope.$watch(     function(scope) {       return scope.avalue;     },     function(newvalue, oldvalue, scope) { }   );