vue-data-scooper - A Vue.js plugin for data initialization

Synopsis

As the official Vue.js document says:

v-model will ignore the initial value, checked or selected attributes found on any form elements. (https://vuejs.org/v2/guide/forms.html)

However, you can initialize the Vue instance data from form elements with this plugin.

Usage

Suppose that we have the following <form> element within a HTML document:

<form id="customer-form">
  <input type="text" v-model="customer.name" name="customer[name]" value="john">
  <input type="radio" v-model="customer.plan" name="customer[plan]" value="A" checked>
  <input type="radio" v-model="customer.plan" name="customer[plan]" value="B">
  <input type="hidden" name="customer[approved]" value="0">
  <input type="checkbox" v-model="customer.approved" name="customer[approved]"
    value="1" checked>
  <select v-model="customer.gender" name="customer[gender]">
    <option value="" selected>Unspecified</option>
    <option value="female">Female</option>
    <option value="male">Male</option>
  </select>
  <textarea v-model="customer.remarks" name="customer[remarks]">Good</textarea>
</form>

Then, we can mount a Vue instance on it.

import Vue from 'vue/dist/vue.esm'
import VueDataScooper from "vue-data-scooper"

Vue.use(VueDataScooper)

document.addEventListener("DOMContentLoaded", () => {
  new Vue({
    el: "#customer-form"
  })
})

The above code works as if you wrote as follows:

import Vue from 'vue/dist/vue.esm'

document.addEventListener("DOMContentLoaded", () => {
  new Vue({
    el: "#customer-form",
    data: {
      customer: {
        name: "john",
        plan: "A",
        approved: true,
        gender: "",
        remarks: "Good"
      }
    }
  })
})

Note that the <form> element must be an actual HTML element, not a Vue template. You cannot use this plugin for the string specified as the template option of a Vue component. See "How this plugin works" section below.

Installation

npm install vue-data-scooper

Background on which this plugin was created

The Vue.js version 1 allows us to provide initial values to the v-model via value attribute, but this functionality was deprecated on the version 2.0.

Migration guide says:

v-model no longer cares about the initial value of an inline value attribute. For predictability, it will instead always treat the Vue instance data as the source of truth.

And, Evan You (the creator of Vue.js) explains about this deprecation:

In Vue 2.0, the template is like a function: it gets called every time something changes. With this in mind, having an inline value is basically saying the input's value is static and should never change - which doesn't make sense when you are using v-model with it. (vuejs/vue#3924 (comment))

Although, as he suggests, we can embed the form values in the HTML document, that solution is rather cumbersome for Rails app developers. For this reason, I created this plugin.

How this plugin works

This plugin provides a function to be set to the data option of Vue components.

Firstly, this function gets the list of DOM elements with v-model attribute within the root element of Vue component:

const root = document.querySelector(this.$options.el)
const inputs = root.querySelectorAll("[v-model]")

Then, iterating through this list, it creates an object (a nested hash). The following abbreviated code illustrates the basic mechanism:

const obj = {}
for (let i = 0; i < inputs.length; i++) {
  let path = el.getAttribute("v-model")

  set(obj, path, el.value)
}

The function set is imported from the lodash. With this function, we can convert <input type="text" v-model="user.name" value="alice"> to { user: { name: "alice" } }.

Note that this plugin collects data using browser's DOM manipulation methods, such as DocumentFragment.querySelectorAll() and Element.getAttribute(). For that reason, the <form> element must be an actual HTML element, not a Vue template.

getInitialData function

This package exports the getInitialData function to extract initial data from the DOM tree.

Here is an example of its usage:

import { getInitialData } from "vue-data-scooper"

let template = `
  <form>
    <input type='text' v-model='user.name' value='Alice'>
    <input type='checkbox' v-model='user.approved' checked>
  </form>
`

let parser = new DOMParser(template)
let doc = parser.parseFromString(template, "text/html")
getInitialData(doc) // => { user: { name: 'Alice', approved: true } }

Development Setup

# install dependencies
yarn install

# test
yarn test

You need the Google Chrome version 59 or higher to run test. If you use google-chrome-beta, export CHROME_BIN environment variable:

export CHROME_BIN=$(which google-chrome-beta)

Building for distribution

yarn build

See Also

• vue-remote-template
• vue-rails-form-builder

License

vue-data-scooper is released under the MIT License.

Author

Tsutomu Kuroda