Build a discount extension

Learn how to develop a scaffolded POS UI extension into a simple discount extension.

Intro

This tutorial shows you how to use the `pos.home.tile.render` and `pos.home.modal.render` [extension targets](/docs/api/pos-ui-extensions/targets) to build a simple POS UI extension that quickly applies discounts to items in the cart. You'll develop the scaffolded extension into a smart grid tile that becomes enabled when the cart reaches a total value. When tapped, the tile opens a modal that presents buttons representing available discounts. When tapped, these buttons apply a discount to the cart and present a toast for notification of success. ![POS UI Extensions Discount Example App](/assets/api/pos/pos-ui-extensions-discount-example.gif)

What you'll learn

In this tutorial, you'll learn how to do the following tasks: - Enable or disable the tile based on cart contents. - Add buttons to the modal that apply a discount and show a toast when tapped. - Give your extension a useful description. - Deploy your extension to Shopify, create a version, and publish.

Requirements

- You've completed the [Getting started with POS UI extensions](/docs/api/pos-ui-extensions/getting-started) guide.

Sample code

The sample code imports some extension components to build the UI. The tile contains the logic to control its enablement based on the cart subtotal. The modal contains the logic to apply discounts based on button tap. You can copy and paste the following code into your index file. You can also update your extension's configuration file following the `shopify.extension.toml` example. The rest of the tutorial walks through this sample code step-by-step.

Discount extension

import React, { useState } from 'react';

import { Tile, useApi, reactExtension } from '@shopify/ui-extensions-react/point-of-sale';

const SmartGridTile = () => {
  const api = useApi<'pos.home.tile.render'>();

  const shouldEnable = (subtotal: string): boolean => {
    return Number(subtotal) > 100
  }

  // You can use the initial cart value to set up state
  const [enabled, setEnabled] = useState(shouldEnable(api.cart.subscribable.initial.subtotal));

  // You can subscribe to changes in the cart to mutate state
  api.cart.subscribable.subscribe((cart) => {
    setEnabled(shouldEnable(cart.subtotal));
  });

  return (
    <Tile
      title='Discount Example App'
      subtitle='React'
      onPress={api.action.presentModal}
      enabled={enabled}
    />
  );
};

export default reactExtension('pos.home.tile.render', () => {
  return <SmartGridTile />
})

import React from 'react';

import { CartDiscountType } from '@shopify/ui-extensions/point-of-sale'
import { ScrollView, Button, Navigator, Screen, useApi, reactExtension } from '@shopify/ui-extensions-react/point-of-sale';

const SmartGridModal = () => {
  const api = useApi<'pos.home.modal.render'>();

  const onButtonPress = (type: CartDiscountType, title: string, amount: string) => {
    // You can apply a discount through the cart API
    api.cart.applyCartDiscount(type, title, amount);

    // You can show a toast to notify the user of something
    api.toast.show('Discount applied');
  }

  return (
    <Navigator>
      <Screen name='Discounts' title='Available Discounts'>
        <ScrollView>
          <Button title='25%' onPress={() => onButtonPress('Percentage', '25% off', '25')} />
          <Button title='$10' onPress={() => onButtonPress('FixedAmount', '$10 off', '10')} />
        </ScrollView>
      </Screen>
    </Navigator>
  )
}

export default reactExtension('pos.home.modal.render', () => {
  return <SmartGridModal />
})

import {extension, Tile} from '@shopify/ui-extensions/point-of-sale';

export default extension('pos.home.tile.render', (root, api) => {
  const shouldEnable = (subtotal: string): boolean => {
    return Number(subtotal) > 100;
  };
  // You can use the initial cart value to set up state
  const tile = root.createComponent(Tile, {
    title: 'Discount Example App',
    subtitle: 'Javascript',
    enabled: shouldEnable(api.cart.subscribable.initial.subtotal),
    onPress: api.action.presentModal,
  });

  // You can subscribe to changes in the cart to mutate state
  api.cart.subscribable.subscribe((cart) => {
    tile.updateProps({enabled: shouldEnable(cart.subtotal)});
  });

  root.append(tile);
});

import {
  extension,
  Screen,
  Button,
  CartDiscountType,
  ScrollView,
} from '@shopify/ui-extensions/point-of-sale';

export default extension('pos.home.modal.render', (root, api) => {
  const onButtonPress = (
    type: CartDiscountType,
    title: string,
    amount: string,
  ) => {
    // You can apply a discount through the cart API
    api.cart.applyCartDiscount(type, title, amount);

    // You can show a toast to notify the user of something
    api.toast.show('Discount applied');
  };

  let mainScreen = root.createComponent(Screen, {
    name: 'Discounts',
    title: 'Available Discounts',
  });
  let scrollView = root.createComponent(ScrollView);

  const percentageDiscountButton = root.createComponent(Button, {
    title: '25%',
    onPress: () => {
      onButtonPress('Percentage', '25% off', '25');
    },
  });

  const fixedAmountDiscountButton = root.createComponent(Button, {
    title: '$10',
    onPress: () => {
      onButtonPress('FixedAmount', '$10 off', '10');
    },
  });

  scrollView.append(percentageDiscountButton);
  scrollView.append(fixedAmountDiscountButton);
  mainScreen.append(scrollView);
  root.append(mainScreen);
});

Step 1: Enable or disable the tile based on cart contents

You can enable or disable the tile based on cart contents by accessing its `subscribable`. In the tile code, initialize state based on the `initial` value of the `subscribable`.

Enable the tile based on cart contents

const [enabled, setEnabled] = useState(shouldEnable(api.cart.subscribable.initial.subtotal));

const tile = root.createComponent(Tile, {
  title: 'Discount Example App',
  subtitle: 'Javascript',
  enabled: shouldEnable(api.cart.subscribable.initial.subtotal),
  onPress: api.action.presentModal
});

Step 2: Subscribe to cart changes

In the tile code, subscribe to cart changes and mutate state based on the updated cart.

Subscribe to cart changes

api.cart.subscribable.subscribe((cart) => {
  setEnabled(shouldEnable(cart.subtotal));
});

api.cart.subscribable.subscribe((cart) => {
  tile.updateProps({ enabled: shouldEnable(cart.subtotal) });
})

Step 3: Add buttons to the modal that apply a discount and display a toast when tapped

You can add buttons to the modal that trigger some action on press. Create the buttons on the modal. Note that most components belong in a ScrollView.

Add buttons to the modal

<ScrollView>
  <Button title='25%' onPress={() => onButtonPress('Percentage', '25% off', '25')} />
  <Button title='$10' onPress={() => onButtonPress('FixedAmount', '$10 off', '10')} />
</ScrollView>

const percentageDiscountButton = root.createComponent(Button, {
  title: '25%',
  onPress: () => { onButtonPress('Percentage', '25% off', '25') }
});

const fixedAmountDiscountButton = root.createComponent(Button, {
  title: '$10',
  onPress: () => { onButtonPress('FixedAmount', '$10 off', '10') }
});

scrollView.appendChild(percentageDiscountButton);
scrollView.appendChild(fixedAmountDiscountButton);

Step 4: Define onPress

Define an `onPress` function to apply the discount and show the toast.

Define onPress

onPress={() => onButtonPress('FixedAmount', '$10 off', '10')}

const onButtonPress = (type: DiscountType, title: string, amount: string) => {
  api.cart.applyCartDiscount(type, title, amount);
  api.toast.show('Discount applied');
};

Step 5: Give your extension a useful description

Your extension's description will be visible to the merchant when they discover and add it to their POS. ![Extension description](/assets/apps/pos/ui-ext-description.png) When you generate a POS UI Extension from Shopify CLI, the extension description defaults to the name of the extension. You can update the description in the generated `toml` file (`shopify.extension.toml`).

Description configuration

...
name = "Loyalty discount"
handle = "Loyalty discount"
description = "Add loyalty discount"
...

Step 6: Deploy and release

Refer to [Deploy app extensions](/docs/apps/deployment/app-versions) for more information.

Next steps

- [Debug](/docs/apps/pos/ui-extensions/debugging) POS UI Extension. - Learn more about building with POS UI extensions by exploring the [POS UI extension reference](/docs/api/pos-ui-extensions).