feat($compile): add isFirstChange() method to onChanges object

[petebacondarwin]

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

Feature

What is the current behavior? (You can also link to an open issue here)

Fixes #14318

What is the new behavior (if this is a feature change)?

Adds isFirstChange() method to changes objects

Does this PR introduce a breaking change?

No - although there is now an extra onChanges call if items are not updated during the first digest since the bindings were defined.

Please check if the PR fulfills these requirements

• The commit message follows our guidelines: https://github.com/angular/angular.js/blob/master/CONTRIBUTING.md#commit-message-format
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

Other information:

Closes #14318

[thorn0]

Is $onChanges called before or after $onInit?

[gkalpak]

@thorn0, before $onInit. Isn't that how ng2 does it as well ?

@petebacondarwin, LGTM (despite some whitespace inconsistencies 😛 )

[petebacondarwin]

@thorn0 - it seems that A2 does it this way: https://angular.io/docs/ts/latest/api/core/OnChanges-interface.html

@gkalpak - it passes JSCS :-P

[petebacondarwin]

@gkalpak - fixed the white-space incongruities

[thorn0]

it seems that A2 does it this way

Although it does (see a plunk), this order doesn't look reasonable to me. :) But that's an issue for the A2 project...

[petebacondarwin]

@thorn0 - I think the idea is that you can choose to ignore this "pre-init" ngChanges by checking the isFirstChange() method. But maybe you are suggesting that they only added that BECAUSE it was too difficult to ensure that this first change hook was not called.

[thorn0]

I just have doubts about the idea of calling anything on a not fully initialized component. As for the initial call of $onChanges in general, I think it's a good thing. For example, for use cases when the component has 'calculated' properties that depend on bindings.