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Allow Button to receive configuration via JavaScript #2867

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merged 7 commits into from
Sep 26, 2022
Merged

Allow Button to receive configuration via JavaScript #2867

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812ad37
Refactor button test
romaricpascal Sep 20, 2022
583c7fe
Safeguard Button from instantiation without element
romaricpascal Sep 20, 2022
8d5577a
Allow button to receive configuration via JavaScript
romaricpascal Sep 20, 2022
86292d7
Allow setting Button config through `initAll`
romaricpascal Sep 20, 2022
413248d
Render data-prevent-double-click explicitely in Nunjucks template
romaricpascal Sep 20, 2022
01d2304
Test that data attributes take precendence over JS config
romaricpascal Sep 20, 2022
a9c6143
Fix typos and poor naming
romaricpascal Sep 26, 2022
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3 changes: 2 additions & 1 deletion src/govuk/all.mjs
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Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,7 @@ import Tabs from './components/tabs/tabs.mjs'
* @param {Object} [config]
* @param {HTMLElement} [config.scope=document] - scope to query for components
* @param {Object} [config.accordion] - accordion config
* @param {Object} [config.button] - button config
* @param {Object} [config.notificationBanner] - notification banner config
*/
function initAll (config) {
Expand All @@ -36,7 +37,7 @@ function initAll (config) {

var $buttons = $scope.querySelectorAll('[data-module="govuk-button"]')
nodeListForEach($buttons, function ($button) {
new Button($button).init()
new Button($button, config.button).init()
})

var $characterCounts = $scope.querySelectorAll('[data-module="govuk-character-count"]')
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34 changes: 29 additions & 5 deletions src/govuk/components/button/button.mjs
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Original file line number Diff line number Diff line change
@@ -1,20 +1,46 @@
import { mergeConfigs, normaliseDataset } from '../../common.mjs'
import '../../vendor/polyfills/Event.mjs' // addEventListener and event.target normaliziation
import '../../vendor/polyfills/Function/prototype/bind.mjs'

var KEY_SPACE = 32
var DEBOUNCE_TIMEOUT_IN_SECONDS = 1

function Button ($module) {
/**
* JavaScript enhancements for the Button component
*
* @class
* @param {HTMLElement} $module - The element this component controls
* @param {Object} config
* @param {Boolean} [config.preventDoubleClick=false] - Whether the button should prevent double clicks
*/
function Button ($module, config) {
if (!$module) {
return this
}

this.$module = $module
this.debounceFormSubmitTimer = null

var defaultConfig = {
preventDoubleClick: false
}
this.config = mergeConfigs(
defaultConfig,
config || {},
normaliseDataset($module.dataset)
)
}

/**
* Initialise component
*/
Button.prototype.init = function () {
if (!this.$module) {
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Asking for clarification:

At the start of the module we're checking for the existence of $module, and only if it exists does the code to assign $module to this.$module run.

Here we are then checking for the existence of this.$module, however wouldn't the previous steps ensure that this statement would never evaluate to false?

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Unfortunately we need that extra check in init because the first check only shortcuts the constructor, to safeguard the access ot the module's dataset. The addEventListener calls happen inside init() fail if the component was instantiated with an undefined/null element.

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If the constructor was called with an undefined element, wouldn't we want to immediately halt execution anyway?

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I don't think there's anything we can do from the constructor to stop the init function from being called – that's happening outside of the object (new govukButton($module).init()).

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Do you mean letting the JS throw an Error when trying to access $module.dataset in the constructor?

We had to set a safety for that in the ErrorSummary to avoid making a breaking change for users that may have a mis-initialised ErrorSummary component. For ex. with a blanket new ErrorSummary(document.querySelector('[data-module="error-summary"]')) that runs on a page without an error summary. With the current version, their code wouldn't break, so we wanted to keep that happening after we added the configuration. I'd be quite keen to remove that safety in the next breaking version as it'll be more informative to users to have an error in their console.

For consistency, I've set that same mechanism on the Button, but need the checks in the two places because of the two step initialisation of components (instantiation + init()).

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Sorry Ollie, I was commenting on an old version of the page and hadn't seen you'd replied.

I don't think there's anything we can do from the constructor to stop the init function from being called – that's happening outside of the object (new govukButton($module).init()).

We could always make init() a no-op in the constructor. That would keep everything in the same place. That'd actually make the thing quite portable from component to component.

if (!$module) {
   // Make `init` a no-op to avoid potentially breaking code at initialisation
   // from lack of HTML element 
   this.init = function(){}
   return this
}

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@romaricpascal romaricpascal Sep 22, 2022 •
edited
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I'll actually update the PR with that approach as:

  • it'll avoid the awkward second check that prompted @querkmachine's question
  • it'll be easy to pass from one component to another

I'll open a second PR to amend the components we've already made configurable.

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I'm not 100% sure about this from a code readability perspective – appreciate at the minute the init function is near the constructor but I think it'd be easy to miss and I don't think I'd expect a class method to be redefined in this way…

If I was writing this I think I'd stick with the two guard clauses we had before, especially if we plan to get rid of the init function in the short-to-mid term.

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Happy to reset to the previous commit, it's not a solution I was particularly attached to and it'll become irrelevant when we remove the init function. Just thought it'd make sense to keep everything in a single place instead of the double check, especially as it's for handling an "error" scenario.

return
}

this.$module.addEventListener('keydown', this.handleKeyDown)
this.$module.addEventListener('click', this.debounce)
this.$module.addEventListener('click', this.debounce.bind(this))
}

/**
Expand Down Expand Up @@ -46,10 +72,8 @@ Button.prototype.handleKeyDown = function (event) {
* @param {MouseEvent} event
*/
Button.prototype.debounce = function (event) {
var target = event.target

// Check the button that was clicked has preventDoubleClick enabled
if (target.getAttribute('data-prevent-double-click') !== 'true') {
if (!this.config.preventDoubleClick) {
return
}

Expand Down
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