> For the complete documentation index, see [llms.txt](https://devworkshops.gitbook.io/masteringvuejs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://devworkshops.gitbook.io/masteringvuejs/dynamic-forms-and-validation/simple-validation.md).

# Simple Validation

## Add validation checks

The first step is to create a `validate` method that will run validation checks against a given category. Any failed validation checks will result in user-friendly messages being added to an `errors` object. These messages can be displayed, and then corrected by the user.

Within **CategoryList.vue**, add a new `errors` object to the `data` property:

{% code title="CategoryList.vue" %}

```javascript
...
data() {
        return {
            errors: null,
...
```

{% endcode %}

Then add a `validate` method as follows:

{% code title="CategoryList.vue" %}

```javascript
...
methods: {
    validate(category) {
        this.errors = {}

        if (!category.name || !category.name.trim()) {
            this.errors.name = 'Name is a required field'
        }
        if (!category.description || !category.description.trim()) {
            this.errors.description = 'Description is a required field'
        }

        // If no errors added, set errors to null
        if (Object.keys(this.errors).length === 0) {
            this.errors = null
        }
    },
...
```

{% endcode %}

Run the validation checks when adding a new category:

{% code title="CategoryList.vue" %}

```javascript
...
add() {
    this.validate(this.addingCategory)
    if (this.errors) {
        return
    }
...
```

{% endcode %}

## Display validation messages

With validation checks completed, you simply need to update the template to display validation error messages. Update template as follows:

{% code title="CategoryList.vue" %}

```markup
...
<template slot="bottom-row">
  <td>
    <input type="text" v-model="addingCategory.name" 
      placeholder="Name..." class="form-control"
      :class="{ 'is-invalid': errors && errors.name }">
    <div class="invalid-feedback" v-if="errors && errors.name">
      {{ errors.name }}
    </div>
  </td>
  <td>
    <input type="text" v-model="addingCategory.description" 
      placeholder="Description..." class="form-control"
      :class="{ 'is-invalid': errors && errors.description }">
    <div class="invalid-feedback" v-if="errors && errors.description">
      {{ errors.description }}
    </div>
  </td>
...
```

{% endcode %}

Save changes and verify that invalid categories cannot be added to the list:

![](/files/-Lg50MPmJQpkKJOpgKQM)


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