OnChange

The On Change operation monitors a single input and passes it to the output only when the value differs from the last successfully outputted value. If the input has not changed, the execution path stops, preventing redundant downstream processing.

Inputs

Port	Type	Required	Description
In	Any	Yes	The value to monitor for changes. Compared against the internally stored last output value.

Outputs

Port	Type	Default	Description
Out	Mirrors In	(unset until first run)	Receives the input value when a change is detected. Unchanged otherwise. Output type matches whatever In is connected to.

Properties

This operation has no configurable properties. Behaviour is determined entirely by input and internal state.

Its Node carries the On Error verb every fallible Operation carries — see the Error Handling guide.

State on Reload

Internal state and output are preserved across restarts within the configured time window. The operation resumes change detection accurately from the restored state.

Strict equality

Comparison uses strict equality — both value and data type must match for “no change” to be detected. Subtle differences in structure for arrays or maps will register as a change.

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How It Works

1. Receive input — The operation receives the In value.

2. Compare — The input is compared against the internally stored last output value using strict equality. On the very first execution (or after a state reset), the input is always considered a change.

3. Change detected — The input value is passed to Out, stored as the new last output value, and the execution path continues.

4. No change — The output remains unchanged and the execution path stops, preventing downstream operations from executing.

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Examples

Data format

All inputs and outputs use MessagePack internally. The examples below show values in JSON notation for readability.

First Run

In: "Hello"

No previous value exists. Input is treated as a change.

Out: "Hello" — path continues.

Value Changes

In: "World"   (last output was "Hello")

"World" differs from "Hello".

Out: "World" — path continues.

No Change

In: "World"   (last output was "World")

No change detected.

Out: "World" (unchanged) — path stops.

Change After Stop

In: "NewValue"   (last output was "World")

"NewValue" differs from "World".

Out: "NewValue" — path continues.

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Use Cases

• Optimizing workflows by only processing data when it actually changes.
• Reducing redundant database writes, log entries, or alert notifications.
• Filtering stable sensor readings from noisy data streams.

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Limitations

• The path-stopping behaviour on “no change” is built-in and cannot be disabled.
• If the input is missing, the Node fails and its On Error verb resolves the failure; under the default verb the branch stops and the output retains its previous value.