Expressions

Use expressions to set node parameters dynamically based on data from:

• Previous nodes
• The workflow
• Your Mosaic Workflows environment

You can execute JavaScript within an expression.

Mosaic Workflows uses a templating language called Tournament, and extends it with data transformation functions that help with common tasks, such as retrieving data from other nodes.

Mosaic Workflows supports two libraries:

• Luxon , for working with data and time.
• JMESPath , for querying JSON.

Writing expressions

To use an expression to set a parameter value:

1. Hover over the parameter where you want to use an expression.
2. Select Expressions in the Fixed/Expression toggle.
3. Write your expression in the parameter, or select Open expression editor to open the expressions editor. If you use the expressions editor, you can browse the available data in the Variable selector . All expressions have the format {{ your expression here }} .

Example: Get data from webhook body

Consider the following scenario: you have a webhook trigger that receives data through the webhook body. You want to extract some of that data for use in the workflow.

Your webhook data looks similar to this:

[
  {
    "headers": {
      "host": "ts-wf.instance.address",
      ...
    },
    "params": {},
    "query": {},
    "body": {
      "name": "Jim",
      "age": 30,
      "city": "New York"
    }
  }
]

In the next node in the workflow, you want to get just the value of city. You can use the following expression:

{{$json.body.city}}

This expression:

1. Accesses the incoming JSON-formatted data using Mosaic Workflows's custom $json variable.
2. Finds the value of city (in this example, "New York"). Note that this example uses JMESPath syntax to query the JSON data. You can also write this expression as {{$json['body']['city']}} .

Example: Writing longer JavaScript

An expression contains one line of JavaScript. This means you can do things like variable assignments or multiple standalone operations.

To understand the limitations of JavaScript in expressions, and start thinking about workarounds, look at the following two pieces of code. Both code examples use the Luxon date and time library to find the time between two dates in months, and encloses the code in handlebar brackets, like an expression.

However, the first example isn't a valid Mosaic Workflows expression:

// This example is split over multiple lines for readability
// It's still invalid when formatted as a single line
{{
  function example() {
    let end = DateTime.fromISO('2017-03-13');
    let start = DateTime.fromISO('2017-02-13');
    let diffInMonths = end.diff(start, 'months');
    return diffInMonths.toObject();
  }
  example();
}}

While the second example is valid:

{{DateTime.fromISO('2017-03-13').diff(DateTime.fromISO('2017-02-13'), 'months').toObject()}}