Remove ES6 code to fix old browser compatibility

[evanlok]

Number.isInteger is not supported on older browsers. babel polyfill fixes compatibility.

https://caniuse.com/#feat=es6-number

[dhilt]

@evanlok Thanks a lot for the PR!

I'm investigating the difference. The main bundle size is being increased from 58 to 96 Kb. Replacing Number.isInteger with a simplest polyfill I'm getting 95 Kb with babel-plugin-transform-runtime plugin enabled. So what are the others 37 Kb? Do we really need babel-plugin-transform-runtime if Number.isInteger is the only problem?

[evanlok]

@dhilt It looks like transform-runtime includes the entire polyfill and not just the ones used in the source code. I couldn't find any configuration that would change the behavior unfortunately. I've refactored this to implement isInteger function in a util module which should make the size increase negligible. I don't know if there is other ES6 code being used, but the changes I've made are working for me on IE11.

[dhilt]

@evanlok oh, Angular already has all necessary stuff for such a refactoring, may I ask you to replace following things in ./src folder?

• isInteger (Number.isInteger) --> angular.isNumber
• Array.isArray --> angular.isArray
• Object.assign --> angular.extend

I believe it should be enough to cover IE 9+ and then I will accept PR.

[evanlok]

@dhilt I've refactored the functions you specified above. I'm assuming there won't be any side effects from using isNumber instead of isInteger?

[dhilt]

@evanlok A good question. Let me think a bit, maybe I'll return your util method. I have to leave for some days, then I'll make a release. Accepting this PR, thanks!