Welcome PR

It's very welcome your pull requests:

• Comments as much as possible.
• Commit message format follow: [AngularJS's commit message convention]
• Cover the unit test for your change

What is AngularJS's commit message convention?

in shortly:

• if you want to commit a feature: feat: bla bla bla
• if you want to commit a fix: fix: bla bla bla
• if you want to commit some script not affect the code logic: chore: bla bla bla
• if you want to commit some logic just on demo project: demo: bla bla bla
• if you want to commit some logic improve performance: prefs: bla bla bla
• if you want to commit some logic just on test: tests: bla bla bla

Helpful explain