UDF not working

If you want to use this as a "Function" without creating a standard measure for every visual, you must use the DEFINE syntax in the DAX Query View.

​Step 1: The "Function" Definition

​You cannot use createOrReplace. Instead, use the DEFINE VAR syntax. This allows the logic to act as a function within the scope of your query.

DEFINE
    -- This acts as your "UDF" logic
    MEASURE 'Table'[XU.Sparkline.MinMax] = 
    VAR LineColour = "#0078D4"
    VAR MaxColour = "#228B22"
    VAR MinColour = "#DC143C"
    VAR PointColour = "%23FFFFFF"
    
    -- Your SVG Logic here...
    VAR MaxX = [MaxX_Logic] 
    VAR MaxY = [MaxY_Logic]
    
    RETURN 
    "data&colon;image/svg+xml;utf8,<svg ...>" & 
    "<circle cx='" & MaxX & "' cy='" & 50 - MaxY & "' ... />" & 
    "</svg>"

-- This part executes the "Function"
EVALUATE
SUMMARIZECOLUMNS(
    'Table'[Category],
    "Sparkline", 'Table'[XU.Sparkline.MinMax]
)

Step 2: Why the createOrReplace syntax is failing

​The createOrReplace syntax is part of TMSL (Tabular Model Scripting Language) or C# scripts used in Tabular Editor—it is not valid DAX code that can be pasted into the formula bar.

• ​If using Power BI Desktop: Use a Measure.
• ​If using Tabular Editor: Use the Scripting window to deploy the measure to the model metadata.

​Step 3: Handling the SVG String

​To ensure the "UDF" output renders as an image:

1. ​Ensure the return string starts with data:image/svg+xml;utf8,.
2. ​Ensure you have escaped the # symbol as %23 if your colors aren't rendering in certain browsers.

​Technical Summary

​While Power BI doesn't have a specific "UDF" object, the DAX Query View is the designated environment for defining and testing function-like logic before committing it to the model as a Measure.