Function optional

docs/app/js/sanddance-app.js:138053–138055

(f)

parcelHelpers.export(exports, "optional", ()=>optional);
parcelHelpers.export(exports, "required", ()=>required);
function optional(f) {
    return f == null ? null : required(f);
}
function required(f) {
    if (typeof f !== "function") throw new Error;
    return f;