Illustrator JavaScript count area with offset.

I see, you have to make the shape to be able to query its Area.

here's a script that adds the offset path, you can delete it after getting the area if you don't need it.

Select ONE shape before running

// apply offset path to selected pathItem
//https://community.adobe.com/t5/illustrator/illustrator-javascript-count-area-with-offset/td-p/11564739?page=1

function main () {
    var idoc = app.activeDocument;
    var sel = idoc.selection[0];

    app.userInteractionLevel = UserInteractionLevel.DONTDISPLAYALERTS;

    var mm = 72/25.4;
    var offset = 5*mm;
    
    // offset path Effect with Round Joins
    var xmlstringOffsetPath = '<LiveEffect name="Adobe Offset Path"><Dict data="R mlim 4 R ofst value I jntp 2 "/></LiveEffect>'; // 0 = round, 1=bevel, 2=miter
    xmlstringOffsetPath = xmlstringOffsetPath.replace("value", offset);

    idoc.selection = null;
    
    var dup = sel.duplicate(sel, ElementPlacement.PLACEAFTER);
    try {
        dup.filled = false;
    }
    catch(e) {}

    dup.selected = true; // select it before applying effects
    
    // apply offset path Effect
    dup.applyEffect(xmlstringOffsetPath);
    app.redraw();
    
    // expand appearance
    app.executeMenuCommand ('expandStyle');
    
    app.userInteractionLevel = UserInteractionLevel.DISPLAYALERTS; 
}

main();

 Carlos