Disable polyfills in tranform-runtime to prevent dupplicate polyfills.

This issue was also discussed here - https://forum.vuejs.org/t/multiple-promise-libraries-being-exported-in-webpack/6610. My thanks to @LinusBorg

Setup

Module	Version
Node.js	6.9.2
npm	4.3
vue-cli	2.8.1
vue	2.1.10
webpack	2.2.1
babel	6.22

Issue details

I have a modified version of the vue-js webpack template which I migrated to webpack 2(some time back) and also made other changes. I have added es6-promise for use with vuex as it needs a Promise library implementation. When I recently used webpack-bundle-analyzer, I saw something odd. A snippet from the vendor.js:

The promise library polyfill is being exported twice. From the discussion with Linus, we were able to conclude that this is happening due to babel-plugin-transform-runtime which, among other things, also introduces polyfills for things likeMap and Promise. This section from babel-loader README is quite relevant but I failed to solve the issue with the bootstrap suggested. Linus suggested that the babel config could be changed to not add polyfills by default:

"plugins": [
  ["transform-runtime", { "polyfill": false}]
]

Are there any polyfills required by vue, vuex and vue-router? I will also try to get rid of the polyfills and check if something breaks.

[LinusBorg]

I’m not sure yet weither we want to remove it completely. the helpers part of the plugin is useful, leaving it ouot could clutter the transpiled modules with duplicated helper code.

[LinusBorg]

No, that’s not what I meant. What I mean is:

If we remove the tranform-runtime (or deactivate the automatic polyfill feature it provides), then you, the developer, have to manually keep track of the polyfill-requiring ES6 features you use include those polyfills if you want to make your app work with out-of-date browsers.

I think we can counter-balance that by switching the es2015 preset for babel-preset-env, especially this feature of that preset, so users can easily add the polyfills that their target browser needs. Maybe that could even be a new option in the setup process.