# Volatile functions

If you work with spreadsheet software regularly, then you've probably heard about Volatile Functions. They are distinctive because they affect the way the calculation engine works. Every cell dependent on a volatile function is recalculated upon every worksheet change triggered by the operations listed below (volatile actions).

HyperFormula uses a dependency tree to keep track of all related cells and ranges of cells. On top of that, it constructs a calculation chain which determines the order in which the recalculation process should be done.

Usually, only cells marked as "dirty" are calculated selectively. However, this is not the case when a volatile function exists somewhere within the workbook. Volatile functions are always treated as "dirty" and recalculated on most actions.

Depending on how many cells are dependent directly or indirectly on the volatile function, it may impact the engine's performance. Use them with caution, especially in large workbooks.

# Volatile functions

Volatile functions are recalculated on every volatile action, regardless of the arguments passed in the function call. Functions that depend on the structure of the sheet act as if they were volatile but only on operations on the sheet structure, such as adding or removing rows or columns.

# Built-in volatile functions:

  • RAND
  • NOW

# Built-in functions that depend on the structure of the sheet:

  • ROW
  • ROWS

See the complete list of functions available.

# Volatile actions

These actions trigger the recalculation process of volatile functions:

Description Related method
Recalculate on demand rebuildAndRecalculate
Resume an automatic recalculation mode resumeEvaluation
Batch operations batch
Modify cell content setCellContents
Modify sheet content setSheetContent
Clear sheet content clearSheet
Insert a row addRows
Remove a row removeRows
Insert a column addColumns
Remove a column removeColumns
Move a cell moveCells
Move a row moveRows
Move a column moveColumns
Add a defined name addNamedExpression
Modify a defined name changeNamedExpression
Remove a defined name removeNamedExpression
Add a sheet addSheet
Remove a sheet removeSheet
Rename a sheet renameSheet
Undo undo
Redo redo
Cut cut
Paste paste

# Tweaking performance

The extensive use of volatile functions may cause a performance drop. To reduce the negative effect, you can try batching these operations.

# Volatile custom functions

There is a way to mark a custom function as volatile:

// this is an example of how the RAND function is implemented
// you can do the same with a custom function
  'RAND': {
      method: 'rand',
      isVolatile: true,

You can find more information about creating custom functions in this section.