node-red-contrib-json

A powerful Node-RED nodes for processing JSON objects.

Install

From your node-red directory:

npm install node-red-contrib-json

Note: the jq engine needs to be able to find and run the jq command line program. See the jq site for installation instructions.

Usage

Create a new contrib-json node, then configure it by chooing an engine and specifying an expression.

Whenever a message arrives, the node will apply the expression using the selected engine. The output is then sent via the outgoing msg.payload.

Engines

These engines are currently supported. Examples of each are integrated into the node itself.

JSONSelect

Site: JSONSelect

This is the default engine. JSONSelect uses a CSS-like selector syntax. Outputs a (possibly empty) array of results.

Why use JSONSelect?

• The syntax is simple to learn and use.

Be careful: Like CSS, recursive descent is the default behavior.

JSONPath

Site: JSONPath

Uses an XPath-like selector syntax. Outputs a (possibly empty) array of results.

Why use JSONPath?

• Relatively simple syntax.
• Supports filter expressions so you can compare values for matching.

jq

Site: jq

Uses a rich custom compositing language, which includes functions and operators for manipulating data. Outputs one or more messages (one for each result).

Why use jq?

• Rich built-in functions for manipulating JSON objects.
• Supports piping operations.

Be careful: this engine shells out to a command-line process, which incurs a JSON serialization and deserialization penalty.

json-select

Site: json-select

Uses a JSONStream based path (or equivalent JSON object) to match and manipulate objects. Outputs a message containing the result (may be an array).

Why use json-select?

• Possible to create composite objects by reaching in to the original.
• For simple jobs, the syntax is very terse.