json-merge

The json-merge transform combines multiple upstream JSON payloads into one object. Inputs are merged in runtime order. Only values that parse as JSON participate (objects by default).

When to use it

Use json-merge to assemble configuration fragments, API responses, or transform outputs from parallel branches before json-template, json-filter, or dashboard nodes.

Limitations

Does not publish dashboards or $heat-dataservice payloads.
Arrays are ignored unless allowArrays is true (shallow: last array wins; deep: replace or concat per arrayMergeMode).
Scalars are skipped unless includeNonObjectJson wraps them under scalarWrapKey.
With outputWhenNoValidJson: fail, the node fails when no input parses; default is an empty object {}.

Configuration (summary)

Property	Default	Description
`mode`	`shallow`	`shallow` or `deep` nested object merge
`allowArrays`	`false`	Allow JSON arrays as inputs
`arrayMergeMode`	`replace`	`replace` or `concat` when `allowArrays` and `mode: deep`
`includeNonObjectJson`	`false`	Wrap scalars as `{ "value": ... }`
`parseMode`	`strict`	`strict` or `lenient` (trim embedded JSON strings)
`outputWhenNoValidJson`	`emptyObject`	`emptyObject` or `fail`
`emitContentMd5`	`false`	Opt-in. Publish through an explicit upload with the merged bytes’ `md5` on the output configuration. Core API skips rescheduling children on a byte-identical republish only when the producer stamped `md5`; the default return path never does, so every upstream tick re-runs every consumer of the merge (on a 9-parent merge feeding a 100KB+ Arbex dashboard script this dominated ingest). Bytes and destination are unchanged: the node `dataSourceName`, else the runner default store.
`settleSeconds`	`0`	Opt-in. Wait until no parent has changed its current output for this many seconds (capped at 60) before merging, so a fan-in burst becomes one publish instead of one per parent. Pair with `emitContentMd5`: the follow-up run Core schedules then finds identical bytes and completes without publishing, so consumers run once per quiet period.

Example


{
  "mode": "deep",
  "allowArrays": false
}

HEAT documentation team. Last updated 2 October 2026.

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