Disabling Submit button if Form fields have not changed in a Nuxt/Vue app

This blog was originally published on RavSam blog.

Forms are one of the most important aspects of any application. It is considered a good UX practice to keep the Save/Submit button disabled until the form contents have not changed. In this blog, we will take a look at how can we accomplish this behaviour in a Nuxt/Vue app.

Creating a Form Template

Let us create a simple form that will help us to understand the concepts of computed and watch properties. In our index.vue in the pages directory, let us add the following form template:

<template>
  <form>
    <label>Name</label>
    <input v-model='form.name' />

    <label>Age</label>
    <input v-model='form.age' />

    <button :disabled="!changed">Save</button>
  <form>
</template>

Let us understand the above template. We have bound our form data model to form inputs using v-model. In our Save button, we will disable it if the form fields have not changed.

Writing Vuex Code

In this example, we will use Vuex Store’s state, actions and mutations to store state and fetch our form data.

// initialize the state variables
export const state = () => ({
  form: {}
})

export const actions = {
  // action to setup form data
  // we can also do an api call as well
  init({ commit }) {
    const data = {
      name: 'Ravgeet',
      age: '21',
    }

    // commit mutuation for changing the state
    commit('setFormData', data)
  }
}

export const mutations = {
  // mutation to change the state
  setFormData(state, data) {
    state.form = data
  }
}

Writing Computed and Watch properties

Our template and Vuex Store are set. Now is the time to implement our application logic in our template’s script. In our pages/index.vue, let us add the following code:

<script>
import _ from 'lodash'

export default {
  data() {
    return {
      changed: false, // useful for storing form change state
      form: {}, // data variable to store current form data binding
    }
  },

  computed: {
    // store the original form data
    originalForm() {
      return this.$store.state.form
    }
  },

  watch: {
    // by watching the original form data
    // create a clone of original form data
    // and assign it to the form data variable
    originalForm() {
      this.form = _.cloneDeep(this.originalForm)
    },

    // watch the changes on the form data variable
    form: {
      handler() {
        // using lodash to compare original form data and current form data
        this.changed = !_.isEqual(this.form, this.originalForm)
      },
      // useful to watch deeply nested properties on a data variable
      deep: true,
    },
  },

  created() {
    // dispatch an action to fill the store with data
    this.$store.dispatch('init')
  }
}
</script>

In our computed and watch properties, we need to clone and compare JS objects. Lodash is a great library for working with JS objects and we will install the same by doing:

$ npm install --save lodash

Now that we have written our code, let us understand what is happening in the above code.

• When the component is created, an action init is dispatched using a created hook. This action causes a mutation in the store and fills the form state variable.

• The value of the computed property, originalForm is calculated as it is dependent upon form state variable.

• As the value of originalForm is being watched using watch hook, the code inside it is executed. A deep clone of originalForm is made and assigned to form data variable.

• Since the value of form is being watched, we use a handler and deep property to run our business logic. We simply check whether the form and originalForm variables are equal using Lodash.

At first, it looks like something very complex is going on but once we break down the things it makes sense.

Results

Let us navigate to our browser and check whether we have been able to achieve our purpose of disabling the form submit button if the form fields have not changed at all.

Voila! We have successfully implemented our workflow. This adds to the UX of our application and saves the user from the frustration especially in long forms.

Thanks for reading 💜

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