Getting Error Cannot read properties of undefined (reading 'eventHelper') For Calling Custom Event

I'm trying to call Custom Event from a Javascript function below

define(["datagrid/DemoDataGridProvider"], function (DemoDataGridProvider) {
"use strict";

class PageModule {
constructor(context) {
this.eventHelper = context.getEventHelper();
}

onBeforeEditEndPO(event) {



  // If edit cancelled → do nothing

  if (event.detail.cancelEdit) {

    return;

  }


  const editable = event.target.querySelector(".editable");

  if (!editable) {

    return;

  }


  const newValue = editable.value;

  const cellContext = event.detail.cellContext;

  const columnIndex = cellContext.indexes.column;



  cellContext.data.data = newValue;

// FIRE CUSTOM EVENT
this.eventHelper.fireCustomEvent("Test", {
value: Number(newValue),
rowIndex: cellContext.indexes.row,
columnIndex: cellContext.indexes.column
});

}

}

return PageModule;

I have a Custom Event 'Test'

Im getting Below Error :

Cannot read properties of undefined (reading 'eventHelper')