How to use the @hpcc-js/other.Persist.widgetArrayWalker function in @hpcc-js/other

callback(widget);
                }
            });
        }
        if (this._prev_ddlUrl && this._prev_ddlUrl !== this.ddlUrl()) {
            //  DDL has actually changed (not just a deserialization)
            this
                .clearContent()
                ;
        }
        this._prev_ddlUrl = this.ddlUrl();
        this._prev_databomb = this.databomb();

        //  Gather existing widgets for reuse  ---
        const widgetArr = [];
        Persist.widgetArrayWalker(this.content(), function (w) {
            widgetArr.push(w);
        });
        const widgetMap = d3Map(widgetArr, function (d) {
            return d.id();
        });
        const removedMap = d3Map(widgetArr.filter(function (d) { return d.id().indexOf(d._idSeed) !== 0 && d.id().indexOf("_pe") !== 0; }), function (d) {
            return d.id();
        });

        const context = this;
        this._marshaller = new HipieDDL.Marshaller()
            .proxyMappings(this.proxyMappings())
            .clearDataOnUpdate(this.clearDataOnUpdate())
            .propogateClear(this.propogateClear())
            .missingDataString(this.missingDataString())
            .widgetMappings(widgetMap)