maestro
2.2510
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Migrate Maestro processes from C# to JavaScript expressions as UiPath deprecates C# for a unified scripting experience.
Purpose
This page helps you move existing Maestro processes from C# expressions to JavaScript expressions. UiPath is deprecating C# as an expression language in Maestro to provide a unified scripting experience, modern syntax highlighting, and broader compatibility with other Automation Suite components.
What this change means
- C# expressions continue to work and are fully supported until they are officially removed in a future release.
- New Maestro projects and features now use JavaScript expressions by default.
- We recommend that you migrate existing expressions to JavaScript to ensure forward compatibility.
If you see a yellow alert message, it means your project currently uses the older C# expression editor. You can continue working with your existing expressions, but we recommend starting to migrate them to JavaScript.
Key differences at a glance
| Concept | C# syntax | JavaScript syntax | Notes |
|---|---|---|---|
| String concatenation | "Hello " + name | "Hello " + name | Identical in both languages. |
| Case conversion | userName.ToUpper() | userName.toUpperCase() | Method name uses lowercase toUpperCase. |
| Equality | amount == 100 | amount === 100 | Use === for strict equality. |
| Null or empty | string.IsNullOrEmpty(x) | !x or x === "" | JavaScript treats null and undefined as falsy. |
| Collections length | items.Count | items.length | Property name differs. |
| Conditional expression | amount > 5000 ? "High" : "Low" | amount > 5000 ? "High" : "Low" | Same syntax in both languages. |
| String interpolation | $"Hello {name}" | `Hello ${name}` | Use backticks (`) for template literals. |
| Date now | DateTime.Now | new Date() | Use the JavaScript Date object. |
| Math | Math.Round(x) | Math.round(x) | Function names are lowercase in JavaScript. |
How to update existing expressions
- Open the Expression Editor for each affected property or gateway condition.
- Copy the C# expression and adapt it using JavaScript syntax (refer to the table Key differences at a glance).
- Use Test in the editor to confirm the result.
- Save and republish your process.
Tip:
When migrating complex formulas, validate variable names and ensure all string comparisons use ===.
Example migration
Before (C#)
vars.total = items.Sum(x => x.Price);
if (vars.total > 10000) vars.priority = "High";
vars.total = items.Sum(x => x.Price);
if (vars.total > 10000) vars.priority = "High";
After (JavaScript)
vars.total = items.reduce((sum, x) => sum + x.Price, 0);
if (vars.total > 10000) vars.priority = "High";
vars.total = items.reduce((sum, x) => sum + x.Price, 0);
if (vars.total > 10000) vars.priority = "High";
Frequently used equivalents
| Common action | C# | JavaScript |
|---|---|---|
| Check multiple conditions | (a && b) || c | (a && b) || c |
| Parse number | int.Parse(x) | parseInt(x) |
| Convert to string | value.ToString() | String(value) |
| Round to 2 decimals | Math.Round(x, 2) | Number(x.toFixed(2)) |
| Compare ignoring case | name.Equals("UIPath", StringComparison.OrdinalIgnoreCase) | name.toLowerCase() === "uipath" |
Testing tips
- Use the Test button in the Expression editor to confirm outputs.
- Watch for differences in null handling and type coercion (
===vs==). - Strings and numbers automatically convert in JavaScript; use explicit casts if accuracy is critical.
Next steps
- Start writing new expressions in JavaScript.
- Update existing processes over time using this guide.
- Plan for migration using either Autopilot or manual translation.
- Track future release notes for the eventual removal of C# expressions.