Implementation of the stripe custom checkout in a vue component (see: https://stripe.com/docs/payments/quickstart)

stripe-checkout.vue

<template>
    <form id="payment-form" @submit.prevent="handleSubmit">
      <div id="payment-element">
        <!--Stripe.js injects the Payment Element-->
      </div>
      <button id="submit" v-if="!(isLoading)">
        <div class="spinner hidden" id="spinner"></div>
        <span id="button-text">Pay now</span>
      </button>
      <div id="payment-message" class="hidden"></div>
    </form>
</template>

<script>
import {loadStripe} from '@stripe/stripe-js/pure';
export default {
  data() {
    return {
      elements: null,
      stripe: null,
      items: [{ id: "xl-tshirt" }],
    }
  },
  methods: {
    handleSubmit: async function(e) {
      e.preventDefault();
      this.setLoading(true);
      const elements = this.elements
      const { error } = await this.stripe.confirmPayment({
        elements,
        confirmParams: {
          // Make sure to change this to your payment completion page
          return_url: "http://localhost:3000/success",
        },
      });

      // This point will only be reached if there is an immediate error when
      // confirming the payment. Otherwise, your customer will be redirected to
      // your `return_url`. For some payment methods like iDEAL, your customer will
      // be redirected to an intermediate site first to authorize the payment, then
      // redirected to the `return_url`.
      if (error.type === "card_error" || error.type === "validation_error") {
        this.showMessage(error.message);
      } else {
        this.showMessage("An unexpected error occured.");
      }

      this.setLoading(false);
      this.isLoading = false;

    },
    showMessage: function (messageText) {
      const messageContainer = document.querySelector("#payment-message");

      messageContainer.classList.remove("hidden");
      messageContainer.textContent = messageText;

      setTimeout(function () {
        messageContainer.classList.add("hidden");
        messageText.textContent = "";
      }, 4000);
    },
    setLoading: function(isLoading) {
      if (isLoading) {
        // Disable the button and show a spinner
        document.querySelector("#submit").disabled = true;
        document.querySelector("#spinner").classList.remove("hidden");
        document.querySelector("#button-text").classList.add("hidden");
      } else {
        document.querySelector("#submit").disabled = false;
        document.querySelector("#spinner").classList.add("hidden");
        document.querySelector("#button-text").classList.remove("hidden");
      }
    }
  },

  async mounted () {
    const stripe = await loadStripe("YOUR_TEST_PUBLIC_TOKEN")
    this.stripe = stripe
    initStripe.bind(this)();
    checkStatus.bind(this)();

    async function initStripe() {
      const items = this.items
      const response = await fetch("/create-payment-intent", {
        method: "POST",
        headers: { "Content-Type": "application/json" },
        body: JSON.stringify({ items }),
      });
      const { clientSecret } = await response.json();

      const appearance = {
        theme: 'stripe',
      };
      this.elements = stripe.elements({ appearance, clientSecret });

      const paymentElement = this.elements.create("payment");
      paymentElement.mount("#payment-element");
    }


    async function checkStatus() {
      const clientSecret = new URLSearchParams(window.location.search).get(
        "payment_intent_client_secret"
      );

      if (!clientSecret) {
        return;
      }

      const { paymentIntent } = await stripe.retrievePaymentIntent(clientSecret);

      switch (paymentIntent.status) {
        case "succeeded":
          this.showMessage("Payment succeeded!");
          break;
        case "processing":
          this.showMessage("Your payment is processing.");
          break;
        case "requires_payment_method":
          this.showMessage("Your payment was not successful, please try again.");
          break;
        default:
          this.showMessage("Something went wrong.");
          break;
      }
    }


        // ------- UI helpers -------

  },

}
</script>

<style scoped>
  /* Variables */
  * {
    box-sizing: border-box;
  }

  body {
    font-family: -apple-system, BlinkMacSystemFont, sans-serif;
    font-size: 16px;
    -webkit-font-smoothing: antialiased;
    display: flex;
    justify-content: center;
    align-content: center;
    height: 100vh;
    width: 100vw;
  }

  form {
    width: 30vw;
    min-width: 500px;
    align-self: center;
    box-shadow: 0px 0px 0px 0.5px rgba(50, 50, 93, 0.1),
      0px 2px 5px 0px rgba(50, 50, 93, 0.1), 0px 1px 1.5px 0px rgba(0, 0, 0, 0.07);
    border-radius: 7px;
    padding: 40px;
  }

  .hidden {
    display: none;
  }

  #payment-message {
    color: rgb(105, 115, 134);
    font-size: 16px;
    line-height: 20px;
    padding-top: 12px;
    text-align: center;
  }

  #payment-element {
    margin-bottom: 24px;
  }

  /* Buttons and links */
  button {
    background: #5469d4;
    font-family: Arial, sans-serif;
    color: #ffffff;
    border-radius: 4px;
    border: 0;
    padding: 12px 16px;
    font-size: 16px;
    font-weight: 600;
    cursor: pointer;
    display: block;
    transition: all 0.2s ease;
    box-shadow: 0px 4px 5.5px 0px rgba(0, 0, 0, 0.07);
    width: 100%;
  }
  button:hover {
    filter: contrast(115%);
  }
  button:disabled {
    opacity: 0.5;
    cursor: default;
  }

  /* spinner/processing state, errors */
  .spinner,
  .spinner:before,
  .spinner:after {
    border-radius: 50%;
  }
  .spinner {
    color: #ffffff;
    font-size: 22px;
    text-indent: -99999px;
    margin: 0px auto;
    position: relative;
    width: 20px;
    height: 20px;
    box-shadow: inset 0 0 0 2px;
    -webkit-transform: translateZ(0);
    -ms-transform: translateZ(0);
    transform: translateZ(0);
  }
  .spinner:before,
  .spinner:after {
    position: absolute;
    content: "";
  }
  .spinner:before {
    width: 10.4px;
    height: 20.4px;
    background: #5469d4;
    border-radius: 20.4px 0 0 20.4px;
    top: -0.2px;
    left: -0.2px;
    -webkit-transform-origin: 10.4px 10.2px;
    transform-origin: 10.4px 10.2px;
    -webkit-animation: loading 2s infinite ease 1.5s;
    animation: loading 2s infinite ease 1.5s;
  }
  .spinner:after {
    width: 10.4px;
    height: 10.2px;
    background: #5469d4;
    border-radius: 0 10.2px 10.2px 0;
    top: -0.1px;
    left: 10.2px;
    -webkit-transform-origin: 0px 10.2px;
    transform-origin: 0px 10.2px;
    -webkit-animation: loading 2s infinite ease;
    animation: loading 2s infinite ease;
  }

  @-webkit-keyframes loading {
    0% {
      -webkit-transform: rotate(0deg);
      transform: rotate(0deg);
    }
    100% {
      -webkit-transform: rotate(360deg);
      transform: rotate(360deg);
    }
  }
  @keyframes loading {
    0% {
      -webkit-transform: rotate(0deg);
      transform: rotate(0deg);
    }
    100% {
      -webkit-transform: rotate(360deg);
      transform: rotate(360deg);
    }
  }

  @media only screen and (max-width: 600px) {
    form {
      width: 80vw;
      min-width: initial;
    }
  }
</style>