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
• RANDBETWEEN
• NOW
• TODAY

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

• COLUMN
• ROW
• COLUMNS
• ROWS
• FORMULATEXT

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.