in indigo.js [685:692]
IndigoObject.prototype.mapMolecule = function(molecule) {
this.d._setSessionId();
let newobj = this.d._checkResult(this.d._lib.indigoMapMolecule(this.id, molecule.id));
if (newobj === 0 || newobj === -1)
return null;
else
return new IndigoObject(this.d, newobj, this);
};