Determination javascript using Gov.UK recommended style

... and without jQuery.

app/views/layouts/application.html.haml

@@ -25,7 +25,7 @@
         %script
           != ga_outlet
 
-  %body{ class: "govuk-template__body controller-#{controller.controller_name}" }
+  %body{ class: "govuk-template__body controller-#{controller.controller_name} govuk-frontend-supported" }
     :javascript
       document.body.className = ((document.body.className) ? document.body.className + ' js-enabled' : 'js-enabled');
 

app/views/shared/_determinations_form.html.haml

@@ -18,7 +18,7 @@
             %div
               = validation_error_message(@error_presenter, :determinations)
 
-      = govuk_table( id: 'determinations', class: 'js-cw-claim-assessment', data: { apply_vat: "#{claim.apply_vat}", vat_url: vat_path(format: :json), submitted_date: claim.vat_date(:db), scheme: claim.agfs? ? 'agfs' : 'lgfs' }) do
+      = govuk_table( id: 'determinations', class: 'js-cw-claim-assessment', data: { module: 'govuk-determination', apply_vat: "#{claim.apply_vat}", vat_url: vat_path(format: :json), submitted_date: claim.vat_date(:db), scheme: claim.agfs? ? 'agfs' : 'lgfs' }) do
         = govuk_table_caption(class: 'govuk-visually-hidden') do
           %h3.govuk-heading-m
             = t('.assessment_summary')

app/webpack/javascripts/modules/determination.js

@@ -0,0 +1,78 @@
+/**
+ * Component name
+ */
+export class Determination {
+  /**
+   * @param {Element} $module - HTML element to use for component
+   */
+  constructor($module) {
+    if (!($module instanceof HTMLElement) || !document.body.classList.contains('govuk-frontend-supported')) {
+      return this
+    }
+
+    this.$module = $module
+
+    // Code goes here
+  }
+
+  /**
+   * Initialise component
+   */
+  init() {
+    // Check that required elements are present
+    if (!this.$module) {
+      return
+    }
+
+    // Code goes here
+    const $module = this.$module
+
+    this.$totalExclVat = document.getElementsByClassName('js-total-exc-vat-determination')[0]
+    this.$totalVat = $module.getElementsByClassName('js-vat-determination')[0]
+    this.$LgfsVat = $module.getElementsByClassName('js-lgfs-vat-determination')[0]
+    this.$totalInclVat = $module.getElementsByClassName('js-total-determination')[0]
+    this.scheme = $module.dataset.scheme
+    // Should this be this.applyVat?
+    this.ajaxVat = $module.dataset.applyVat
+    this.vatUrl = $module.dataset.vatUrl
+    this.vatDate = $module.dataset.submittedDate
+
+    this.fields = [
+      document.getElementById('claim_assessment_attributes_fees'),
+      document.getElementById('claim_assessment_attributes_expenses'),
+      document.getElementById('claim_assessment_attributes_disbursements'),
+      document.getElementById('claim_assessment_attributes_vat_amount')
+    ].filter(field => field)
+    this.fields.forEach(element => element.addEventListener('change', async () => await this.calculateTotalRows()))
+  }
+
+  async calculateTotalRows() {
+    const total = this.fields.reduce((n, field) => n + this.parsedValue(field), 0).toFixed(2)
+    const data = await this.applyVat(total)
+    this.$totalExclVat.innerHTML = data.net_amount
+    if (this.$totalVat) { this.$totalVat.innerHTML = data.vat_amount }
+    this.$totalInclVat.innerHTML = data.total_inc_vat
+  }
+
+  parsedValue(field) {
+    const value = parseFloat(field?.value)
+    if (value) {
+      return Math.max(0.0, value)
+    } else {
+      return 0.0
+    }
+  }
+
+  async applyVat(netAmount) {
+    const params = new URLSearchParams({
+      scheme: this.scheme,
+      lgfs_vat_amount: this.$LgfsVat?.value,
+      date: this.vatDate,
+      apply_vat: this.ajaxVat,
+      net_amount: netAmount
+    })
+    const response = await fetch(this.vatUrl + '?' + params.toString())
+
+    return await response.json()
+  }
+}

app/webpack/packs/application.js

@@ -36,7 +36,6 @@ import '../javascripts/modules/Modules.ExpensesDataTable.js'
 import '../javascripts/modules/Modules.Debounce.js'
 import '../javascripts/modules/case_worker/admin/Modules.ManagementInformation.js'
 import '../javascripts/modules/case_worker/Allocation.js'
-import '../javascripts/modules/case_worker/claims/DeterminationCalculator.js'
 import '../javascripts/modules/external_users/claims/FeeFieldsDisplay.js'
 import '../javascripts/modules/external_users/claims/DisbursementsCtrl.js'
 import '../javascripts/modules/external_users/claims/FeeTypeCtrl.js'

app/webpack/packs/govuk-frontend.js

@@ -1,6 +1,13 @@
 import '../stylesheets/govuk-frontend.scss'
 
+import { Determination } from '../javascripts/modules/determination.js'
+
 // fonts & images
 require.context('govuk-frontend/govuk/assets', true)
 
+const determinations = document.querySelectorAll('[data-module="govuk-determination"]')
+determinations.forEach((determination) => {
+  new Determination(determination).init()
+})
+
 require('govuk-frontend').initAll()

docs/javascript_restructure.md

@@ -49,4 +49,28 @@ class Example {
 The primary benefits of refactoring our Javascript is to have a single, consistent style so that future developers can better understand the codebase.
 Specifically using the recommended Gov.UK style will further facilitate new developers who have worked on other Gov.UK projects.
 
-This is a *work in progress* so javascript modules may be written in any of the above formats but the ideal is the class design pattern.
+This is a *work in progress* so javascript modules may be written in any of the above formats but the ideal is the class design pattern.
+
+### Removal of jQuery
+
+There has also been a long-standing plan to remove the dependency on jQuery as modern versions of Javascript have all (most?) of the features that jQuery provided. There are some [notes here](https://tobiasahlin.com/blog/move-from-jquery-to-vanilla-javascript/) to help with migrating jQuery to vanilla Javascript and below are some further pointers.
+
+#### Accessing the data of elements
+
+jQuery provides a way of accessing data from elements as follows;
+
+```javascript
+// <table id="determinations" data-scheme="agfs">
+
+table = $('#determinations')
+scheme = table.data('scheme')
+```
+
+Without jQuery this becomes;
+
+```javascript
+// <table id="determinations" data-scheme="agfs">
+
+table = document.getElementById('determinations')
+scheme = table.dataset.scheme
+```