add function types with typescript

typescript-function.types.ts

/**
   * Hide a column if the column field
   * belongs to applicability hidden by default columns
   */
  processLeaf(
    colDef: ColDef,
    columnsSelection: string[],
    leafProcess: (visible: boolean, colDef: ColDef) => ColDef
  ) {
    let colDefChanged: ColDef;
    if (
      (colDef.field && !columnsSelection.includes(colDef.field)) ||
      !colDef.field
    ) {
      colDefChanged = leafProcess(false, colDef);
      return colDefChanged;
    } else {
      colDefChanged = colDef;
      colDefChanged = leafProcess(true, colDef);
      return colDef;
    }
  }