import causes "Unexpected token" error

[Dean-NC]

Uglifyjs 3 does support the import statement, but jscompress.com says:
Unexpected token: name «Z1», expected: punc «;» (line: 1, col: 7)

import Z1 from './z1.js';

function test() {
	Z1.abc();
}

It does work here:
https://skalman.github.io/UglifyJS-online