This is a plugin for Squarespace to add a minimumPriceQuantity option for checkout

minimumPriceQuantity.js

// REQUIREMENTS

// User should be able to set the minimum required price
// User should be able to adjust the error message
// User should be able to change the currency symbol to match their country
// The error message should be temporarily displayed if they are below the order minimum
// The error message should display the required minimum amount
// The error message should disappear once they are above the order minimum
// The error message should appear again if they are below the minimum order amount

var minimumPricePlugin = (function () {
	//
	// Variables 
	//	
	
	var publicAPIs= {};
	
	var settings;	
	// Default settings for plugin
	var defaults = {
		checkoutSelector: '[class*="checkout-button"]',
		cartSubTotalSelector: '[class*="subtotalPrice"]',
		currencySymbol: '$',
		minimumPrice: 50,
		errorMessage() { return `Sorry you're below the minimum order amount ${this.currencySymbol}${this.minimumPrice}` }
	};
	

	
	
	//
	// Methods
	//
	
	// This checks the current cart total and lets you pass an argument for your minimum price
	publicAPIs.minimumPriceCheck = function(minimumPrice) {
		var checkoutButton = document.querySelector(settings.checkoutSelector);
		
		// Get subtotal
		var cartSubTotal = document.querySelector(settings.cartSubTotalSelector);
		var cartTotalString = cartSubTotal.textContent;
		var cartTotalNum = parseFloat(cartTotalString.replace(/[^\d.-]/g,''));

	
		if (cartTotalNum < minimumPrice) {
			
			checkoutButton.disabled = true;
			checkoutButton.style.pointerEvents = 'none';
			checkoutButton.style.cursor = 'not-allowed';
			showErrorMessage();
			console.log('too low')
		} else {
		checkoutButton.disabled = false;
			checkoutButton.style.pointerEvents = 'auto';
			checkoutButton.style.cursor = 'pointer';
			hideErrorMessage();
			console.log('good to go!');
		}
	
	}
	
	
	// Create Error Message
	var addErrorMessage = function (sibling) {
		sibling.insertAdjacentHTML('afterend', `<div class="errorMessage">${settings.errorMessage()}</div>`);
	}	
	
	// Show Error Message
	var showErrorMessage = function() {
		var errorMessage = document.querySelector('.errorMessage');
		errorMessage.style.display = 'block';
	}
	
	// Hide Error Message
	var hideErrorMessage = function() {
		var errorMessage = document.querySelector('.errorMessage');
		errorMessage.style.display = 'none';
	}
	
	//
	// Inits & Event Listeners
	//
	
	
	// Initializes the plugin @param {Object} options 
	
	publicAPIs.init = function(options) {
		// Creates a new settings object from the defaults and user options object
		settings = Object.assign({}, defaults, options);		
		// Get checkout button
		var checkoutButton = document.querySelector(settings.checkoutSelector);
		
		// Get subtotal
		var cartSubTotal = document.querySelector(settings.cartSubTotalSelector);
		console.log(cartSubTotal)
		
		var minimumPrice = settings.minimumPrice;


	
		// Adds error HTML
		addErrorMessage(checkoutButton);
		
			// This is the function that the Mutation Observer will run
		var mutationCallback = mutations => {
		publicAPIs.minimumPriceCheck(settings.minimumPrice)
		console.log("mutations",mutations)
		}
		
		// Creates new mutation observer 
		var observer = new MutationObserver(mutationCallback);
	
		// Mutation Observer configuration
		var mutationConfig = {
			attributes:true,
			characterData:true,
			subtree:true
		};
	
		observer.observe(cartSubTotal, mutationConfig);
			
		publicAPIs.minimumPriceCheck(settings.minimumPrice);
		
	};
	
	
	//
	//	Return Public APIs
	//
	return publicAPIs;
})();



// Initialize plugin
minimumPricePlugin.init();
	


// TODO Ensure that it only watches the checkout page


// String replace method and regex to keep float numbers i.e. $12.49 -> "12.49"
// var s = "-12345.50 €".replace(/[^\d.-]/g, '');