Functions

🧩 Using JavaScript Functions (Advanced)

In addition to built-in expressions, you can write JavaScript functions and invoke them from within the Logic dialog using:

js.eval('fnName', arg1, arg2, ...)

The JavaScript functions must be defined in the following format:

function fnName(args) {
  const arg1 = args[0];
  const arg2 = args[1];
  // your logic
}

⚠️ Note: Arguments are automatically collected as an array, so you should extract individual arguments from the args array in your function body as shown above.

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⚠️ Important Considerations

• JavaScript functions incur a small performance overhead as the expression engine needs to cross into the JavaScript runtime. 👉 Avoid using them in rapidly updating UIs such as scrolling lists or infinite lists. Instead, pre-process the data before passing it to a ListView.

• JavaScript functions that work in the Dashboard preview (browser) might not work in the app for advanced date/time scenarios. This is because the app runtime uses QuickJS, which has limited support for some Date APIs. Use basic Date parsing/formatting only, and prefer Digia’s built-in DateTime functions whenever possible.

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✅ Examples

Define functions in your script:

function multiply(args) {
  const a = args[0];
  const b = args[1];
  return a * b;
}

function formatTimestamp(args) {
  const timestamp = args[0];  // e.g. 1691939250000
  const date = new Date(timestamp);
  return date.toISOString().split('T')[0];  // ✔️ basic date formatting
}

Invoke them in your expression:

js.eval('multiply', 6, 7)

js.eval('formatTimestamp', response.data.createdAt)