According to the documentation on event dispatching event types should follow these rules:

  • No uppercase letters
  • No spaces
  • Use underscores to separate words

When I attempt to use underscores in my event type I don't seem to be able to handle it.


<lightning-button label="Update" onclick={toggleEditAsset}></lightning-button>

toggleEditAsset = () => {
    const event = new CustomEvent('toggle_edit_asset');


<c-asset-information asset={model.asset} edit-asset={editAsset} ontoggleeditasset={handleToggleEditAsset}></c-asset-information>

handleToggleEditAsset() {
    this.editAsset = !this.editAsset

This handler does not get called.

If I try to change ontoggleeditasset to ontoggle_edit_asset I get an error

LWC1056: Invalid event name ontoggle_edit_asset. Event name can only contain lower-case alphabetic characterslwc

If I change the event to toggleeditasset everything works fine

What is the proper markup to handle an event with underscores?

  • Why don't you just leave it as const event = new CustomEvent('toggleeditasset'); That should work and you don't need to worry about anything else. – Nico W Aug 21 '19 at 13:03
  • I wanted to follow best practices where it says Use underscores to separate words. I'm aware I can do that, but I was more curious about how to do it the way the documentation says to do it – TemporaryFix Aug 21 '19 at 16:01

If you want to handle an event type sampleevent in HTML of parent, you should directly add prefix in attribute onsampleevent.

But, You cannot add event handler in HTML with underscores _ as it will not compile.

However, you can do it through JS of parent component:

I would recommend not to create event-types with underscores as it may not even be supported from javascript in future releases (although currently it is able to handle)

connectedCallback() {
    this.template.addEventListener('toggle_edit_asset', this.handleToggle);
handleToggle(e) {
    console.log('toggle_edit_asset handled');

This is Playground link

This will work but you will be getting warning in the console as below:

[LWC warning]: Invalid event type "toggle_edit_asset" dispatched in element . Event name should only contain lowercase alphanumeric characters.


You need to add bubbles:true in event as you need to Bubble an event up inside the containing component’s template.

toggleEditAsset = () => {
    const event = new CustomEvent('toggle_edit_asset', { bubbles: true });

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