Guys I think I did it! The key was here in the ddbell`s post. Here is the code, it takes a folder and a string as parameters:
async function exportWEBP(destinationFolder, fileName) {
let activeDocumentID = app.activeDocument.id;
console.log(activeDocumentID);
let newFile = await destinationFolder.createFile(fileName, { overwrite: true });
let saveWebpFile = await fs.createSessionToken(newFile);
await core.executeAsModal(async () => {
const result = await batchPlay(
[
{
_obj: "save",
as: {
_obj: "WebPFormat",
compression: {
_enum: "WebPCompression",
_value: "compressionLossless"
},
includeXMPData: false,
includeEXIFData: false,
includePsExtras: false
},
in: {
_path: saveWebpFile,
_kind: "local"
},
// fileDoNotAppendCopy: true,
documentID: activeDocumentID,
copy: true,
lowerCase: true,
saveStage: {
_enum: "saveStageType",
_value: "saveBegin"
},
_options: {
dialogOptions: "dontDisplay"
}
}
],
{}
);
}, );
}