Vue: using HTML5 validations

05 Dec 2018

Handling client side validation using the HTML5 validation api is getting easier due to the wide support on modern browsers. With HTML validation api you don’t have install any new package and learn its api.

Remember this might not be apt for your application and use case. Read the detailed incompatibility issues here.

This post doesn’t intent to cover all the use cases and corner cases, but to give intro to using HTML5 apis in a Vue app.

Basic implementation

For the basic version we don’t have to do anything specific to vue. Just need to bind @submit to handleSubmit action will trigger the validation and show error message in native way.

// SimpleForm.vue

<template>
  <div class="section">
    <div class="container">
      <div class="columns">
        <div class="column is-5 is-offset-3">
          <form @submit.prevent="handleSubmit">
            <div class="field">
              <label class="label">Name</label>
              <div class="control">
                <input class="input" type="text" placeholder="Text input" required>
              </div>
            </div>
            <div class="field is-grouped">
              <div class="control">
                <button type="submit" class="button is-link">Submit</button>
              </div>
            </div>
          </form>
        </div>
      </div>
    </div>
  </div>
</template>

<script>
export default {
  name: "SimpleForm",
  methods: {
    handleSubmit() {

    }
  }
}
</script>

Form submit programmatically

When we use form.submit(), it wont trigger the native validations. This requirement usually arise when we want to do some task (like update state) before the form submission. In such cases we have to trigger the validation and report it manually using checkValidity and reportVaidity methods.

<template>
  <div class="section">
    <div class="container">
      <div class="columns">
        <div class="column is-5 is-offset-3">
          <form ref="form" @submit.prevent="handleSubmit">
            <div class="field">
              <label class="label">Name</label>
              <div class="control">
                <input
                  class="input"
                  type="text"
                  placeholder="Text input"
                  required
                />
              </div>
            </div>
            <div class="field is-grouped">
              <div class="control">
                <button type="submit" class="button is-link">Submit</button>
              </div>
              <div class="control">
                <button
                  type="button"
                  class="button is-link"
                  @click="handleSignup"
                >
                  Signup
                </button>
              </div>
            </div>
          </form>
        </div>
      </div>
    </div>
  </div>
</template>

<script>
export default {
  name: "MultipleButton",
  methods: {
    handleSubmit(e) {
      console.log("submit");
    },
    handleSignup() {
      console.log("do task before submit");
      if (this.$refs.form.checkValidity()) {
        this.handleSubmit();
      } else {
        this.$refs.form.reportValidity();
      }
    }
  }
};
</script>

In this case when checkValidity is true we have to call handleSubmit directly since the submit event wont be raised.

Custom design for Error messages

It now we didn’t controlled how the error message are shown to the user. Consider we need to show the error message in a uniform way across the browsers and don’t want to hide those automatically.

In such case we have to bind callback to form invalid event, to collect error message from all the child inputs. We will use validationMessage property on the input element to get the localized message for the validation failure.

<template>
  <div class="section">
    <div class="container">
      <div class="columns">
        <div class="column is-5 is-offset-3">
          <div className="container">
            <form
              @submit="handleSubmit"
              @change="handleChange"
              @invalid.capture.prevent="handleInvalid"
            >
              <div class="field">
                <label class="label">Username</label>
                <div class="control has-icons-left has-icons-right">
                  <input
                    class="input" 
                    :class="errorClass('username')"
                    type="text"
                    placeholder="Name"
                    required
                    name="username"
                  />
                  <span class="icon is-small is-left">
                    <i class="fas fa-user" />
                  </span>
                  <span v-if="fieldErrors.username" class="icon is-small is-right">
                    <i class="fas fa-exclamation-triangle" />
                  </span>
                </div>
                <p v-if="fieldErrors.username" class="help is-danger"></p>
              </div>
              <div class="field">
                <label class="label">Email</label>
                <div class="control has-icons-left has-icons-right">
                  <input
                    class="input"
                    :class="errorClass('email')"
                    type="email"
                    placeholder="Email input"
                    required
                    name="email"
                  />
                  <span class="icon is-small is-left">
                    <i class="fas fa-envelope" />
                  </span>
                  <span v-if="fieldErrors.email" class="icon is-small is-right">
                    <i class="fas fa-exclamation-triangle" />
                  </span>
                </div>
                <p v-if="fieldErrors.email" class="help is-danger"></p>
              </div>
              <div class="field">
                <label class="label">Message</label>
                <div class="control">
                  <textarea
                    class="textarea"
                    :class="errorClass('message')"
                    placeholder="Textarea"
                    required
                    name="message"
                  />
                </div>
                <p v-if="fieldErrors.message" class="help is-danger"></p>
              </div>
              <div class="field">
                <div class="control">
                  <label class="checkbox">
                    <input type="checkbox" required name="toc" />
                    I agree to the <a href="#">terms and conditions</a>
                  </label>
                  <p v-if="fieldErrors.toc" class="help is-danger"></p>
                </div>
              </div>
              <div class="field is-grouped">
                <div class="control">
                  <button class="button is-link">Submit</button>
                </div>
              </div>
            </form>
          </div>
        </div>
      </div>
    </div>
  </div>
</template>

<script>
export default {
  name: "CustomDesign",
  data() {
    return {
      fieldErrors: {}
    }
  },
  methods: {
    handleSubmit() {
      
    },
    handleChange(evt) {
      console.log('handleChange :: ', evt.target.name);
      this.fieldErrors = {
        ...this.fieldErrors,
        [evt.target.name]: ""
      };
    },
    handleInvalid(evt) {
      console.log('handleInvalid :: ', evt.target.name);
      this.fieldErrors = {
        ...this.fieldErrors,
        [evt.target.name]: evt.target.validationMessage
      };
    },
    errorClass(field) {
      return this.fieldErrors[field] ? "is-danger" : ""
    }
  },
}
</script>

In this make sure to use capture modifier like @invalid.capture.prevent since the invalid event won’t bubble.

The working sample is available on codesandbox

Vue HTML5 validation

Versions of Language/packages used in this post.

| Library/Language | Version |
| ---------------- |---------|
|      Vue         |  2.5.2 |

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