This API is reliable and breaking changes are unlikely.
backendApi.expandTop(qRow, qCol, qAll)
Expands the top dimensions of a pivot table. Only works for hypercubes with qMode = P which are not always fully expanded.
If set to true, qRow and qCol are ignored and all cells are collapsed.
A promise of a Qlik Associative Engine reply.
this.backendApi.expandTop( 0, 1 );