[BUG] UglifyJs only works with ES5

Do you want to request a feature or report a bug?

bug

What is the current behavior?

When adding the UglifyJsPlugin, I get an error like

ERROR in global.js from UglifyJs
Unexpected token: name (resolve) [global.js:1218,8]

where the problem like is like this:

function animationFrame() {
    let resolve = null; // <--------------------------------- RIGHT HERE
    const promise = new _promise2.default(function (r) {
        return resolve = r;
    });
    window.requestAnimationFrame(resolve);
    return promise;
}

If the current behavior is a bug, please provide the steps to reproduce.

This is a bug, because not all loaders convert JavaScript to strictly ES5 (which UglifyJs requires). For example, buble-loader can convert JavaScript code for relatively new browser targets, which results in let and const statements that UglifyJs seems to crash on.

What is the expected behavior?

I should be able to stick buble-loader into my Webpack project, and I should be able to use something like UglifyJsPlugin to minify it.

However, this only works if one uses something like Babel to completely convert to ES5.

If this is a feature request, what is motivation or use case for changing the behavior?

Please mention other relevant information such as the browser version, Node.js version, webpack version and Operating System.

I’m on Webpack 3.4.1.

Look how many people have had this problem: https://github.com/joeeames/WebpackFundamentalsCourse/issues/3

[trusktr]

@damsorian just replace webpack/lib/optimize/UglifyJsPlugin with babili-webpack-plugin. You have to npm i babili-webpack-plugin --save-dev first.

[ickyrr]

in my case, this answer helped me.