Append link URL in Google Tag Manager without ECMASCRIPT_2015

Question

The following code works great in browser. It looks for any 'a' tags with an href that includes 'example.com' and the appends it with '&utm_day=monday'. So 'exmaple.com' becomes 'example.com&utm_day=monday'.

<script>
let text = '&utm_day=monday'
document.querySelectorAll('a').forEach(
        item => {
            if (item.href.includes("example.com")) {
                item.href += text
            }
        }
    )
</script>

When trying to inject this code using GTM (Google Tag Manager) I get an error for both the 'let' and the '=>' that says "This language feature is only supported for ECMASCRIPT_2015 mode or better: let declaration."

I assumed using vars would fix this, but my syntax is blah. Any ideas?

<script>
var text = '&utm_day=monday';
var item = document.querySelectorAll('a').forEach;
  if (item.href.includes("example.com")) {
    item.href += text
  }
</script>

Answer 1

forEach is a function that accepts a callback as an argument. you can't just do .forEach

Well, you could, but you're just putting whole forEach function in item. So now item is a function.

Then you try to get attribute href of that function.

Here:

var text = '&utm_day=monday';
document.querySelectorAll('a').forEach(function(item) {
  if (item.href.includes("example.com")) {
    item.href += text;
  }
});