options of minifyJs should to be reviewed

[simonjoom]

use correct option of minifyJs
related to
facebook/create-react-app#4234
to get the "why" Please read this thread upper

specify ecma: 5 like described in create-react-app to support ie11 and to avoid some bug on some browser.

[pieh]

This is interesting. Will need to some research

@jquense do You have any thoughts on that?

[jquense]

seems reasonable tho i'm not sure what it means in terms of output. at the point to which uglify is run the code is already compiled to the desired ecma, i'm not sure if uglify will go out of it's way to upscale syntax unless it's told not too?

in other word's i can see uglify turning multiple let declarations into let foo, bar, baz but i don't think it will decide to use let in the output if the input is already var.

[simonjoom]

i think that just take and copy things without think a lot of investigation from create-react-app is reasonable as it's a very used and debugged repo from Facebook! :)

like explained in facebook/create-react-app#4234 (comment) put down ecma to version 5 in the compression just disable some undesirable optimisation that uglify can create so it's not actually change the version output of the code created. you can still have some ecma2016 code inside

[KyleAMathews]

@jquense perhaps it generates different syntax for newer versions? E.g. some new JS syntax produces smaller output so they opt into that if they can 🤷‍♂️

[shanekenney]

@KyleAMathews correct. Terser does take opportunities to use more compact syntax if the ecma version allows it. E.g. Shorthand object properties raised in issue #9034

Here's the test documenting it:
https://github.com/terser-js/terser/blob/master/test/compress/object.js#L111

use_shorthand_opportunity: {
    beautify = {
        ecma: 6
    }
    input: {
        var foo = 123;
        var obj = {foo: foo};
    }
    expect_exact: "var foo=123;var obj={foo};"
}

[KyleAMathews]

Cool! Great to know. Could someone PR a fix?