build_your_own_angularjs_sample

Build Your Own Angular Chapter 1. Scopes And Digest
Scope.prototype.$digest = function() {
var ttl = 10;
var dirty;
this.$$lastDirtyWatch = null;
do {
while (this.$$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);
};
Now we can be sure the digest will terminate, regardless of whether it’s running because
it’s dirty or because there’s something in its async queue.
Scope Phases
Another thing $evalAsync does is to schedule a $digest if one isn’t already ongoing. That
means, whenever you call $evalAsync you can be sure the function you’re deferring will be
invoked “very soon” instead of waiting for something else to trigger a digest.
For this to work there needs to be some way for $evalAsync to check whether a $digest
is already ongoing, because in that case it won’t bother scheduling one. For this purpose,
Angular scopes implement something called a phase, which is simply a string attribute in
the scope that stores information about what’s currently going on.
As a unit test, let’s make an expectation about a field called $$phase, which should be
“$digest” during a digest, “$apply” during an apply function invocation, and null otherwise:
test/scope_spec.js
it("has a $$phase field whose value is the current digest phase", function() {
scope.aValue = [1, 2, 3];
scope.phaseInWatchFunction = undefined;
scope.phaseInListenerFunction = undefined;
scope.phaseInApplyFunction = undefined;
scope.$watch(
function(scope) {
scope.phaseInWatchFunction = scope.$$phase;
return scope.aValue;
},
function(newValue, oldValue, scope) {
32 ©2014 Tero Parviainen Errata / Submit