How to use the @rdfjs/data-model.variable function in @rdfjs/data-model

if (blankMap[name]) {
          name = blankMap[name];
        } else {
          if (variableNames.indexOf(name) >= 0) {
            // increase index added to name until we find one that is available (2 loops at most)
            let idx = 0;
            while (variableNames.indexOf(name + idx) >= 0) {
              ++idx;
            }
            name = name + idx;
          }
          blankMap[term.value] = name;
          variableNames.push(name);
        }
        changed = true;
        return variable(name);
      } else {
        return term;
      }
    });

public static patternToCountQuery(pattern: RDF.Quad): string {
    return toSparql(ActorRdfResolveQuadPatternSparqlJson.FACTORY.createProject(
      ActorRdfResolveQuadPatternSparqlJson.FACTORY.createExtend(
        ActorRdfResolveQuadPatternSparqlJson.FACTORY.createGroup(
          ActorRdfResolveQuadPatternSparqlJson.patternToBgp(pattern),
          [],
          [ActorRdfResolveQuadPatternSparqlJson.FACTORY.createBoundAggregate(
            variable('var0'),
            'count',
            ActorRdfResolveQuadPatternSparqlJson.FACTORY.createTermExpression(namedNode('*')),
            false,
          )],
        ),
        variable('count'),
        ActorRdfResolveQuadPatternSparqlJson.FACTORY.createTermExpression(variable('var0')),
      ),
      [ variable('count') ],
    ));
  }

public static nullToVariable(term: RDF.Term, label: string): RDF.Term {
    if (!term) {
      return DataFactory.variable('v' + label);
    }
    return term;
  }

public static patternToCountQuery(pattern: RDF.Quad): string {
    return toSparql(ActorRdfResolveQuadPatternSparqlJson.FACTORY.createProject(
      ActorRdfResolveQuadPatternSparqlJson.FACTORY.createExtend(
        ActorRdfResolveQuadPatternSparqlJson.FACTORY.createGroup(
          ActorRdfResolveQuadPatternSparqlJson.patternToBgp(pattern),
          [],
          [ActorRdfResolveQuadPatternSparqlJson.FACTORY.createBoundAggregate(
            variable('var0'),
            'count',
            ActorRdfResolveQuadPatternSparqlJson.FACTORY.createTermExpression(namedNode('*')),
            false,
          )],
        ),
        variable('count'),
        ActorRdfResolveQuadPatternSparqlJson.FACTORY.createTermExpression(variable('var0')),
      ),
      [ variable('count') ],
    ));
  }

return toSparql(ActorRdfResolveQuadPatternSparqlJson.FACTORY.createProject(
      ActorRdfResolveQuadPatternSparqlJson.FACTORY.createExtend(
        ActorRdfResolveQuadPatternSparqlJson.FACTORY.createGroup(
          ActorRdfResolveQuadPatternSparqlJson.patternToBgp(pattern),
          [],
          [ActorRdfResolveQuadPatternSparqlJson.FACTORY.createBoundAggregate(
            variable('var0'),
            'count',
            ActorRdfResolveQuadPatternSparqlJson.FACTORY.createTermExpression(namedNode('*')),
            false,
          )],
        ),
        variable('count'),
        ActorRdfResolveQuadPatternSparqlJson.FACTORY.createTermExpression(variable('var0')),
      ),
      [ variable('count') ],
    ));
  }

public static patternToCountQuery(pattern: RDF.Quad): string {
    return toSparql(ActorRdfResolveQuadPatternSparqlJson.FACTORY.createProject(
      ActorRdfResolveQuadPatternSparqlJson.FACTORY.createExtend(
        ActorRdfResolveQuadPatternSparqlJson.FACTORY.createGroup(
          ActorRdfResolveQuadPatternSparqlJson.patternToBgp(pattern),
          [],
          [ActorRdfResolveQuadPatternSparqlJson.FACTORY.createBoundAggregate(
            variable('var0'),
            'count',
            ActorRdfResolveQuadPatternSparqlJson.FACTORY.createTermExpression(namedNode('*')),
            false,
          )],
        ),
        variable('count'),
        ActorRdfResolveQuadPatternSparqlJson.FACTORY.createTermExpression(variable('var0')),
      ),
      [ variable('count') ],
    ));
  }