=JSONFIFO

The =JSONFIFO() function appends a new JSON object to an existing JSON array while optionally enforcing a maximum array length. When a maximum length is set and exceeded, the oldest entry (first in the array) is automatically removed, maintaining a First-In-First-Out (FIFO) structure.

Syntax

=JSONFIFO(ExistingJsonArray; NewJsonObjectToAdd; MaximumLength)

Parameters

• ExistingJsonArray

  • A JSON array to which a new object will be added.

• NewJsonObjectToAdd

  • A valid JSON object to append to the array.

• MaximumLength

  • The maximum number of objects allowed in the array.

  • Use 0 to indicate no maximum limit.

How It Works

• The new JSON object is appended to the end of the array.

• If the array size exceeds MaximumLength, the oldest object is removed.

• If MaximumLength is 0, the array grows without restriction.

Usage Notes

• Ideal for rolling logs, audit trails, recent activity feeds, and history tracking.

• Automatically manages array size without additional logic.

• Formula function names are case sensitive and must be written in ALL CAPS.

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Examples

Scenario: Activity Log Tracker

Let’s say you’re maintaining an activity log that should only keep the 3 most recent entries.

Initial Setup

// Starting with an existing array of 2 activities
ExistingArray = [
  {"timestamp": "2025-05-30 09:00", "action": "login", "user": "john_doe"},
  {"timestamp": "2025-05-30 09:15", "action": "file_upload", "user": "jane_smith"}
]

Adding a New Entry

// Create new activity object
NewActivity = {"timestamp": "2025-05-30 09:30", "action": "report_generated", "user": "mike_wilson"}

// Add to array with maximum of 3 entries
=JSONFIFO(ExistingArray; NewActivity; 3)

Result

[
  {"timestamp": "2025-05-30 09:00", "action": "login", "user": "john_doe"},
  {"timestamp": "2025-05-30 09:15", "action": "file_upload", "user": "jane_smith"},
  {"timestamp": "2025-05-30 09:30", "action": "report_generated", "user": "mike_wilson"}
]

Adding Another Entry (Triggers FIFO Behavior)

// Add a 4th entry - this will remove the oldest (first) entry
NewActivity2 = {"timestamp": "2025-05-30 09:45", "action": "logout", "user": "john_doe"}

=JSONFIFO([previous result]; NewActivity2; 3)

Final Result

[
  {"timestamp": "2025-05-30 09:15", "action": "file_upload", "user": "jane_smith"},
  {"timestamp": "2025-05-30 09:30", "action": "report_generated", "user": "mike_wilson"},
  {"timestamp": "2025-05-30 09:45", "action": "logout", "user": "john_doe"}
]

Other Use Cases

No Maximum Limit

// Set maximum to 0 for unlimited entries
=JSONFIFO(ProductArray; {"item": "new_product", "price": 29.99}; 0)

Single Entry Queue

// Keep only the most recent entry
=JSONFIFO(StatusArray; {"status": "current"}; 1)

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Keywords

JSONFIFO, JSON array management, FIFO queue, rolling log, activity history, JSON append, workflow logging, formula function