BigCommerce - GA Enhanced Ecommerce Tracking

track.html

<script type="text/javascript">
window.dataLayer = window.dataLayer||[];
function trackGTMEcommerce() {
    this._addTrans = addTrans;
    this._addItem = addItems;
    this._trackTrans = trackTrans;
}

var transaction = {};
transaction.transactionProducts = [];

function addTrans(orderID, store, total, tax, shipping, city, state, country) {
    transaction.transactionId = orderID;
    transaction.transactionAffiliation = store;
    transaction.transactionTotal = total;
    transaction.transactionTax = tax;
    transaction.transactionShipping = shipping;
}


function addItems(orderID, sku, product, variation, price, quantity) {
    transaction.transactionProducts.push({
        'id': orderID,
            'sku': sku,
            'name': product,
            'category': variation,
            'price': price,
            'quantity': quantity
    });
}

function trackTrans() {
    transaction.event = 'transactionSuccess';
    dataLayer.push(transaction);
}

var pageTracker = new trackGTMEcommerce();
</script>
<script>
    (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
    (i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
    m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
    })(window,document,'script','//www.google-analytics.com/analytics.js','ga');

    /* Check for product page - change to reflect current class/id */
    var productPage = document.querySelectorAll('body.page-type-product').length > 0;
    var checkout = window.location.pathname === '/checkout';
    /* Replace with tracker info */
    ga('create', 'UA-XXXXXXXX-1', 'mywebsite.com');
    ga('require', 'ec');
    if (!checkout && !productPage) {
       ga('send', 'pageview');
   }

	/* Checkout */
	if (checkout) {
		/* get the current cart contents */
		const Http = new XMLHttpRequest();
		const url='/api/storefront/carts';
		Http.open("GET", url);
		Http.send();
		Http.onreadystatechange=(e)=>{
			if (Http.readyState === 4) {
				var response = JSON.parse(Http.responseText);
				var cart = response[0].lineItems.physicalItems;
				for(var i = 0; i < cart.length; i++) {
				    var product = cart[i];
				    ga('ec:addProduct', {
				      'id': product.productId,
				      'name': product.name,
				      'price': product.salePrice,
				      'quantity': product.quantity
				    });
			    }
				ga('ec:setAction','checkout', {'step': 1});
				ga('send', 'pageview');
			}
		}
		(e)=>{ 
			console.log(Http.responseText); 
		}

		window.addEventListener("click", function(event){ 
			var id = event.target.id;
			if (id === 'checkout-customer-continue' ) {
				ga('ec:setAction','checkout', {'step': 2});
				ga('send', 'pageview');
			}
			if (id === 'checkout-shipping-continue') {
				ga('ec:setAction','checkout', {'step': 3});
				ga('send', 'pageview');
			}
			if (id === 'checkout-billing-continue') {
				ga('ec:setAction','checkout', {'step': 4});
				ga('send', 'pageview');
			}
			if (id === 'checkout-payment-continue') {
				ga('ec:setAction','checkout', {'step': 5});
				ga('send', 'pageview');
			}
		});

	}

	/* product Page */
 	if (productPage) {
		ga('ec:addProduct', {
		  'id': juitem_pid,
		  'name': juitem_nm
		});
		ga('ec:setAction', 'detail');
		ga('send', 'pageview');
		/* add to cart event - form-action-addToCart */
		document.getElementById("form-action-addToCart").addEventListener("click", function(){ 
			ga('ec:addProduct', {
			    'id': juitem_pid,
			    'name': juitem_nm,
			    'price': juitem_pr,
			    'quantity': document.getElementById('qty[]').value
			  });
			ga('ec:setAction', 'add');
			ga('send', 'event', 'Product', 'click', 'add to cart');     
		});
	}


    function trackEcommerce() {
    this._addTrans = addTrans;
    this._addItem = addItems;
    this._trackTrans = trackTrans;
    }
    function addTrans(orderID,store,total,tax,shipping,city,state,country) {
    ga('ec:setAction', 'purchase', {
        'id': orderID,
        'affiliation': store,
        'revenue': total,
        'tax': tax,
        'shipping': shipping,
        'city': city,
        'state': state,
        'country': country
    });
    }
    function addItems(orderID,sku,product,variation,price,qty) {
    ga('ec:addProduct', {
        'id': orderID,
        'sku': sku,
        'name': product,
        'category': variation,
        'price': price,
        'quantity': qty
    });
    }
    function trackTrans() {
        ga('send', 'pageview');
    }
    var pageTracker = new trackEcommerce();
</script>

How to impement it ??

Anyone guide me how can I implmented it?