hello guys,
having some issue to initalize “act” variable to manage acf_form AJAX submission…
loaded the JS in the file using it:
single.js
import acf from '../../../../../../plugins/advanced-custom-fields-pro/assets/js/acf-input.min';
no errors, on compile but on page load
acf-pro-input.min.js:1 Uncaught ReferenceError: acf is not defined
at acf-pro-input.min.js:1
at Object.<anonymous> (acf-pro-input.min.js:1)
at Object.<anonymous> (acf-pro-input.min.js:1)
at __webpack_require__ (bootstrap f832f27f0a7614de2f52:678)
at fn (bootstrap f832f27f0a7614de2f52:88)
at Object.<anonymous> (single.js:1)
at Object.<anonymous> (single.js:837)
at __webpack_require__ (bootstrap f832f27f0a7614de2f52:678)
at fn (bootstrap f832f27f0a7614de2f52:88)
at Object.<anonymous> (main.js:1)
(anonymous) @ acf-pro-input.min.js:1
(anonymous) @ acf-pro-input.min.js:1
(anonymous) @ acf-pro-input.min.js:1
__webpack_require__ @ bootstrap f832f27f0a7614de2f52:678
fn @ bootstrap f832f27f0a7614de2f52:88
(anonymous) @ single.js:1
(anonymous) @ single.js:837
__webpack_require__ @ bootstrap f832f27f0a7614de2f52:678
fn @ bootstrap f832f27f0a7614de2f52:88
(anonymous) @ main.js:1
(anonymous) @ main.js:29
__webpack_require__ @ bootstrap f832f27f0a7614de2f52:678
fn @ bootstrap f832f27f0a7614de2f52:88
(anonymous) @ addStyles.js:398
__webpack_require__ @ bootstrap f832f27f0a7614de2f52:678
(anonymous) @ bootstrap f832f27f0a7614de2f52:724
(anonymous) @ bootstrap f832f27f0a7614de2f52:724
any hint?
ty!
acf-pro-input.min.js uses an acf global from probably a more general acf.min.js, which then also has to be imported or enqueued (but then declared as a global in eslint/wepback configuration).
ty @strarsis but no good news 
I have updated webpack.config.js according to some older post found here:
externals: {
jquery: 'jQuery',
acf: 'acf',
},
updated the act import, to a more general one:
import acf from '../../../../../../plugins/advanced-custom-fields-pro/pro/assets/js/acf-pro-input';
note this is not imported in main.js but on single.js
but error persists 
Uncaught ReferenceError: acf is not defined
at acf-pro-input.js:3
at Object.<anonymous> (acf-pro-input.js:531)
at Object.<anonymous> (acf-pro-input.js:1853)
at __webpack_require__ (bootstrap e2544497300e4d128db3:678)
at fn (bootstrap e2544497300e4d128db3:88)
at Object.<anonymous> (single.js:1)
at Object.<anonymous> (single.js:834)
at __webpack_require__ (bootstrap e2544497300e4d128db3:678)
at fn (bootstrap e2544497300e4d128db3:88)
at Object.<anonymous> (main.js:1)
assets/js/acf-pro-input- hm, this looks like the JS file for a ACF PRO input field.
ok, tried something different, less… picky 
import acf from '../../../../../../plugins/advanced-custom-fields-pro/assets/js/acf';
this went a bit ahead but, compiled, part of js is loading, but still have some error:
WARINING
jquery.js?ver=3.5.1:4046 jQuery.Deferred exception: __WEBPACK_IMPORTED_MODULE_2__plugins_advanced_custom_fields_pro_assets_js_acf___default.a.addAction is not a function TypeError: __WEBPACK_IMPORTED_MODULE_2__plugins_advanced_custom_fields_pro_assets_js_acf___default.a.addAction is not a function
at HTMLDocument.<anonymous> (https://localhost:3000/app/themes/sage/dist/scripts/main.js:25625:103)
at mightThrow (https://localhost:3000/wp/wp-includes/js/jquery/jquery.js?ver=3.5.1:3762:29)
at process (https://localhost:3000/wp/wp-includes/js/jquery/jquery.js?ver=3.5.1:3830:12) undefined
ERROR:
jquery.js?ver=3.5.1:4055 Uncaught TypeError: __WEBPACK_IMPORTED_MODULE_2__plugins_advanced_custom_fields_pro_assets_js_acf___default.a.addAction is not a function
at HTMLDocument.<anonymous> (single.js:773)
at mightThrow (jquery.js?ver=3.5.1:3762)
at process (jquery.js?ver=3.5.1:3830)
Alright, I checked out the source myself (I am also an owner of ACF PRO) and found out that these script files don’t export JavaScript modules, but rather attach to a global (window) variable.
Hence webpack will not be able to use it as a module - and it doesn’t do these checks during build but rather during runtime.
Therefore you have to import it not as symbol:
require('../../../../../../plugins/advanced-custom-fields-pro/assets/js/acf');
(or import syntax)
You have to configure webpack/ESLINT to expect acf being a global (window) variable (apparently you already did).
Or you just enqueue that script from within your theme/plugin.
ty @strarsis I think I finally managed by enqueing in setup.php.
do you think I may face issues when building and deploying, since I am including from a weird path…
wp_enqueue_script('sage/acf-input.min.js', asset_path('../../../plugins/advanced-custom-fields-pro/assets/js/acf.js'), ['jquery'], null, true);
Technically this is a not an asset path (that is resolved by Sage runtime into an URL) but a plugin url.
Therefore you should use the plugins_url method to enqueue that URL directly:
wp_enqueue_script('sage/acf-input.min.js', plugins_url('advanced-custom-fields-pro/assets/js/acf.js'), ['jquery'], null, true);