index.es.js should be in ES5 + ESModules

[gfx]

This is because webpack's default resolution of main fields is:mainFields: ['browser', 'module', 'main'], which means index.es.js is selected by webpack even if it targets older IEs.

https://webpack.js.org/configuration/resolve/

I've set its value to mainFields: ["browser", "main", "module"] for now in my project, but I think the "module" entry point should be written in ES5 + ESModules, not ES2015 + ESModules.

[yahoocla]

Thank you for submitting this pull request, however I do not see a valid CLA on file for you. Before we can merge this request please visit https://yahoocla.herokuapp.com/ and agree to the terms. Thanks! 😄

[gfx]

Agreed to CLA. Thanks.

[coveralls]

Coverage remained the same at 98.936% when pulling e11b6aa on gfx:es5+esm into 29eea1c on yahoo:master.

[redonkulus]

Isn't it implied that if a browse supports es modules, that it should support ES6+ syntax?

[gfx]

Currently the benefit of providing ESModules for browsers is the tree-shaking by webpack, means webpack downpiles ESModules syntax even if no transpiler (e.g. Babel) is configured.

https://webpack.js.org/guides/tree-shaking/

It relies on the static structure of ES2015 module syntax

As far as I know, most of projects that use webpack are configured not to transpile external libraries, so libraris should be compatible with ES5 if the projects support legacy IEs, except for ESModules syntax because the syntax is transpiled by webpack.

Thus, if a library has "module" field for browsers, it should be ES5 + ESModules. it may feel strange, though.

[JonatanGarciaClavo]

My 2 cents, i detected problems related to that in old Safari browsers that doesn't support const. So this will help me a lot, well it will be expected behaviour if you use this with webpack as @gfx mention before.
Also should be modified following line
const IS_CLIENT = typeof window !== 'undefined';
to be
var IS_CLIENT = typeof window !== 'undefined';

[gfx]

@JonatanGarciaClavo Thanks! Fixed const in e11b6aa

FYI If you use webpack, https://github.com/bitjourney/check-es-version-webpack-plugin should be useful to detect ES2015 in your bundles.

[JonatanGarciaClavo]

@gfx wow thanks for the plugin i didn't know about it, i will use it because my client use IE 11 as supported browser 😞 , that will help me to detect this case in a easy way, not only when i see failure report from app insights hehe.

[JonatanGarciaClavo]

@redonkulus so is there any problem to make this happens? Or are we missing something that can't make it happens?

[redonkulus]

I'm ok with merging this, sorry it took so long.

[redonkulus]

released in v2.0.5

[gfx]

Thanks!

[roderickhsiao]

Thank you!