Maestro user guide

Last updated Feb 18, 2026

Transitioning from C# to JavaScript expressions

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 Cloud 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.

expression editor prompt warning java script

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";

After (JavaScript): 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.