Sudden error in 1 year old function

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It gets weirder: I put some logging in like so:

   datValidFrom = $w('#ddsPropsVIew').getCurrentItem().ptValidFrom;

console.log(" datValidFrom=" + datValidFrom);
console.log(" type datValidFrom=" + typeof datValidFrom);

And in Publish Mode (not Preview) I get this:

datValidFrom=2018-07-01T03:00:00.000Z
console.js:35 type datValidFrom=string

And no, I did not declare it as a string in the Collection.