What does the "a._known.slice is not a function" error message mean?

FranciscoRodriguez2

I have previously used this Arcade expression with other datasets and haven not had any issues, I tried running this expression today: 

var portal = Portal('https://mass-eoeea.maps.arcgis.com');
var features = FeatureSetByPortalItem(portal, 'ed174bb08dc34850ac8d0e719cae0c72', 0, ['*'], true);

var open = $feature;
var landid = contains(open, features);

var cnt = Count(landid);

var resultado = "This Open-Space parcel contains " + cnt+ " "+ "Land ID Points";
for (var f in landid) {
resultado += TextFormatting.NewLine + "Land Id(s):" + text(f.id)
}

return resultado

When I test the expression out in the webmap, I get the expected results:

Result :Value
Result: This Open-Space parcel contains 1 Land ID Points
Land Id(s):10196
Type: String

However, when I try running the expression using  the field calculator on a string field (255 characters) in the $feature, I keep getting this error message, 

a._known.slice is not a function

Can anyone point me in the right direction as to what I am doing wrong with my syntax?

arcade_2.PNG

arcade_1.PNG

add-arcade-expression-set-in-esri-arcgis-experience-builder-into-table-widget.png

Screenshot 2026-07-28 130730.png

XanderBakker

Hi Francisco Rodriguez ,

I have not seen that error before and  to be honest and I don't know why it is happening. 

I do see a couple of things:

• You are retrieving the point layer using  FeatureSetByPortalItem, but you specify all the fields and also the geometry. I think you could optimize the code by using ... , 0, ['id'], false); since you only use the id field afterwards.
• How many point can there be in a polygon. Your text will grow fast since for each ID you add a new line. Wouldn't it be better to present a list of Id's separated by commas?

Something like:

<SPAN class="keyword token">var</SPAN> portal <SPAN class="operator token">=</SPAN> <SPAN class="token function">Portal</SPAN><SPAN class="punctuation token">(</SPAN><SPAN class="string token">'https://mass-eoeea.maps.arcgis.com'</SPAN><SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">;</SPAN>
<SPAN class="keyword token">var</SPAN> features <SPAN class="operator token">=</SPAN> <SPAN class="token function">FeatureSetByPortalItem</SPAN><SPAN class="punctuation token">(</SPAN>portal<SPAN class="punctuation token">,</SPAN> <SPAN class="string token">'ed174bb08dc34850ac8d0e719cae0c72'</SPAN><SPAN class="punctuation token">,</SPAN> <SPAN class="number token">0</SPAN><SPAN class="punctuation token">,</SPAN> <SPAN class="punctuation token">[</SPAN><SPAN class="string token">'id'</SPAN><SPAN class="punctuation token">]</SPAN><SPAN class="punctuation token">,</SPAN> <SPAN class="keyword token">false</SPAN><SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">;</SPAN>

<SPAN class="keyword token">var</SPAN> open <SPAN class="operator token">=</SPAN> $feature<SPAN class="punctuation token">;</SPAN>
<SPAN class="keyword token">var</SPAN> landid <SPAN class="operator token">=</SPAN> <SPAN class="token function">contains</SPAN><SPAN class="punctuation token">(</SPAN>open<SPAN class="punctuation token">,</SPAN> features<SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">;</SPAN>
<SPAN class="keyword token">var</SPAN> cnt <SPAN class="operator token">=</SPAN> <SPAN class="token function">Count</SPAN><SPAN class="punctuation token">(</SPAN>landid<SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">;</SPAN>

<SPAN class="keyword token">var</SPAN> resultado <SPAN class="operator token">=</SPAN> <SPAN class="string token">"This Open-Space parcel contains "</SPAN> <SPAN class="operator token">+</SPAN> cnt <SPAN class="operator token">+</SPAN> <SPAN class="string token">" Land ID Points"</SPAN><SPAN class="punctuation token">;</SPAN>
resultado <SPAN class="operator token">+</SPAN><SPAN class="operator token">=</SPAN> TextFormatting<SPAN class="punctuation token">.</SPAN>NewLine <SPAN class="operator token">+</SPAN> <SPAN class="string token">" - Land Id: "</SPAN><SPAN class="punctuation token">;</SPAN>
<SPAN class="keyword token">var</SPAN> lst <SPAN class="operator token">=</SPAN> <SPAN class="punctuation token">[</SPAN><SPAN class="punctuation token">]</SPAN><SPAN class="punctuation token">;</SPAN>
<SPAN class="keyword token">for</SPAN> <SPAN class="punctuation token">(</SPAN><SPAN class="keyword token">var</SPAN> f <SPAN class="keyword token">in</SPAN> landid<SPAN class="punctuation token">)</SPAN> <SPAN class="punctuation token">{</SPAN>
    lst<SPAN class="punctuation token">[</SPAN><SPAN class="token function">Count</SPAN><SPAN class="punctuation token">(</SPAN>lst<SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">]</SPAN> <SPAN class="operator token">=</SPAN> f<SPAN class="punctuation token">.</SPAN>id<SPAN class="punctuation token">;</SPAN>
<SPAN class="punctuation token">}</SPAN>
resultado <SPAN class="operator token">+</SPAN><SPAN class="operator token">=</SPAN> <SPAN class="token function">Concatenate</SPAN><SPAN class="punctuation token">(</SPAN>lst<SPAN class="punctuation token">,</SPAN> <SPAN class="string token">", "</SPAN><SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">;</SPAN>
<SPAN class="keyword token">return</SPAN> resultado<SPAN class="punctuation token">;</SPAN><SPAN class="line-numbers-rows"><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN></SPAN>