Sapper on Rollup seems to have some difficulties to handle the Typescript from svelte-i18n

[ktryndchrs]

sapper-template-i18n/package.json

Line 18 in 25d44b6

"svelte-i18n": "^3.0.4"

The returned error:

The 'this' keyword is equivalent to 'undefined' at the top level of an ES module, and has been rewritten
4: See the accompanying LICENSE file for terms.
5: */
6: var __assign = (this && this.__assign) || function () {
                   ^
7:     __assign = Object.assign || function(t) {
8:         for (var s, i = 1, n = arguments.length; i < n; i++) {
The 'this' keyword is equivalent to 'undefined' at the top level of an ES module, and has been rewritten
4: See the accompanying LICENSE file for terms.
5: */
6: var __assign = (this && this.__assign) || function () {
                           ^
7:     __assign = Object.assign || function(t) {
8:         for (var s, i = 1, n = arguments.length; i < n; i++) {
The 'this' keyword is equivalent to 'undefined' at the top level of an ES module, and has been rewritten
1: var __extends = (this && this.__extends) || (function () {
                    ^
2:     var extendStatics = function (d, b) {
3:         extendStatics = Object.setPrototypeOf ||
The 'this' keyword is equivalent to 'undefined' at the top level of an ES module, and has been rewritten
1: var __extends = (this && this.__extends) || (function () {
                            ^
2:     var extendStatics = function (d, b) {
3:         extendStatics = Object.setPrototypeOf ||
The 'this' keyword is equivalent to 'undefined' at the top level of an ES module, and has been rewritten
12:     };
13: })();
14: var __spreadArrays = (this && this.__spreadArrays) || function () {
                          ^
15:     for (var s = 0, i = 0, il = arguments.length; i < il; i++) s += arguments[i].length;
16:     for (var r = Array(s), k = 0, i = 0; i < il; i++)
The 'this' keyword is equivalent to 'undefined' at the top level of an ES module, and has been rewritten
12:     };
13: })();
14: var __spreadArrays = (this && this.__spreadArrays) || function () {
                                  ^
15:     for (var s = 0, i = 0, il = arguments.length; i < il; i++) s += arguments[i].length;
16:     for (var r = Array(s), k = 0, i = 0; i < il; i++)
The 'this' keyword is equivalent to 'undefined' at the top level of an ES module, and has been rewritten
4: See the accompanying LICENSE file for terms.
5: */
6: var __spreadArrays = (this && this.__spreadArrays) || function () {
                         ^
7:     for (var s = 0, i = 0, il = arguments.length; i < il; i++) s += arguments[i].length;
8:     for (var r = Array(s), k = 0, i = 0; i < il; i++)
The 'this' keyword is equivalent to 'undefined' at the top level of an ES module, and has been rewritten
4: See the accompanying LICENSE file for terms.
5: */
6: var __spreadArrays = (this && this.__spreadArrays) || function () {
                                 ^
7:     for (var s = 0, i = 0, il = arguments.length; i < il; i++) s += arguments[i].length;
8:     for (var r = Array(s), k = 0, i = 0; i < il; i++)
The 'this' keyword is equivalent to 'undefined' at the top level of an ES module, and has been rewritten
 7: // tslint:disable:no-consecutive-blank-lines
 8: // tslint:disable:align
 9: var __extends = (this && this.__extends) || (function () {
                     ^
10:     var extendStatics = function (d, b) {
11:         extendStatics = Object.setPrototypeOf ||
The 'this' keyword is equivalent to 'undefined' at the top level of an ES module, and has been rewritten
 7: // tslint:disable:no-consecutive-blank-lines
 8: // tslint:disable:align
 9: var __extends = (this && this.__extends) || (function () {
                             ^
10:     var extendStatics = function (d, b) {
11:         extendStatics = Object.setPrototypeOf ||
The 'this' keyword is equivalent to 'undefined' at the top level of an ES module, and has been rewritten
20:     };
21: })();
22: var __assign = (this && this.__assign) || function () {
                    ^
23:     __assign = Object.assign || function(t) {
24:         for (var s, i = 1, n = arguments.length; i < n; i++) {
The 'this' keyword is equivalent to 'undefined' at the top level of an ES module, and has been rewritten
20:     };
21: })();
22: var __assign = (this && this.__assign) || function () {
                            ^
23:     __assign = Object.assign || function(t) {
24:         for (var s, i = 1, n = arguments.length; i < n; i++) {
The 'this' keyword is equivalent to 'undefined' at the top level of an ES module, and has been rewritten
1: var __spreadArrays = (this && this.__spreadArrays) || function () {
                         ^
2:     for (var s = 0, i = 0, il = arguments.length; i < il; i++) s += arguments[i].length;
3:     for (var r = Array(s), k = 0, i = 0; i < il; i++)
The 'this' keyword is equivalent to 'undefined' at the top level of an ES module, and has been rewritten
1: var __spreadArrays = (this && this.__spreadArrays) || function () {
                                 ^
2:     for (var s = 0, i = 0, il = arguments.length; i < il; i++) s += arguments[i].length;
3:     for (var r = Array(s), k = 0, i = 0; i < il; i++)
The 'this' keyword is equivalent to 'undefined' at the top level of an ES module, and has been rewritten
1: var __assign = (this && this.__assign) || function () {
                   ^
2:     __assign = Object.assign || function(t) {
3:         for (var s, i = 1, n = arguments.length; i < n; i++) {
The 'this' keyword is equivalent to 'undefined' at the top level of an ES module, and has been rewritten
1: var __assign = (this && this.__assign) || function () {
                           ^
2:     __assign = Object.assign || function(t) {
3:         for (var s, i = 1, n = arguments.length; i < n; i++) {

The Setup
Sapper-i18n-Rollup.zip

Personnal note
I'll continue to work on it and come back if I ever find the solution

[samcreate]

@ktryndchrs Found this after I read your issue (I was having the same issue)

https://github.com/kaisermann/svelte-i18n/blob/master/docs/FAQ.md

[UltraCakeBakery]

I'm having the exact same issue. I also was reading this: rollup/rollup#1518
Hiding the warning as shown in the link posted above works fine.

It does feel like a hack to hide it. Maybe svelte-i18n codebase should be modified. I know it is not harmful but the warning makes a good point lol.