谷歌分析电子商务与gtag.js成功AJAX / jQuery POST

Question

I need to track purchase event for Google Analytics Ecommerce using gtag.js. For doing that I need to put these sample js code on target page:

gtag('event', 'purchase', {
  'transaction_id': '1234',
  'value': 19.90,
  'items': [
      {
      'id': '12345',
      'name': 'AwesomeT-Shirt',
    },
    ]
});

The problem is that I don't have a target page. I have only a page with AJAX form that could return required values from PHP through created JSON object with array of these values:

//php
$ecomm = array(
    'transaction_id'=>$orderID,
    'value'=>$order_amount,
    'id'=>$productID,
    'name'=>$product_name
    );
echo json_encode($ecomm);

It is working fine. Console in Chrome shows all of required values:

$.ajax({
type: "POST",
url: "...",
data: query,
dataType: 'json',
success: function(data){
    console.log(data.transaction_id); 
    console.log(data.value);
    console.log(data.id);
    console.log(data.name);
}
});

How to modify last js code for replace these:

    console.log(data.transaction_id); 
    console.log(data.value);
    console.log(data.id);
    console.log(data.name);

to these with proper values:

gtag('event', 'purchase', {
  'transaction_id': '2074',
  'value': 19.90,
  'items': [
      {
      'id': '295',
      'name': 'AwesomeT-Shirt',
    },
    ]
});

Thanks.