Added exact as valid modifier

[mokkabonna]

https://vuejs.org/v2/guide/events.html#exact-Modifier

[mysticatea]

Thank you for the PR!

The exact modifier seems to have to use with one or more system modifiers. Could you add the check the exact modifier is used with system modifiers?

For example:

const SYSTEM_MODIFIERS = new Set([
  'ctrl', 'alt', 'shift', 'meta'
})

// ....

         if (modifier === "exact" && !node.key.modifiers.some(SYSTEM_MODIFIERS.has, SYSTEM_MODIFIERS)) {
           context.report({
             node,
             loc: node.loc,
             message: "The 'exact' modifier should be used in combination with other system modifiers."
           })
         }

[mokkabonna]

It's not only for system modifiers.

If I have this:

<div @click.ctrl.exact="handler1" @click="handler2"></div>

handler 2 will be also be triggered when holding ctrl. handler 1 will only be triggered when holding ctrl.

Using exact on both works as expected:

<div @click.ctrl.exact="handler1" @click.exact="handler2"></div>

But I agree the docs give the impression that you got:

The .exact modifier should be used in combination with other system modifiers to indicate that the exact combination of modifiers must be pressed for the handler to fire.

But I have manually tested this and both handlers in the first example are triggered when holding ctrl.

[mysticatea]

Oh, thank you for the explanation! I got it. LGTM.

[mokkabonna]

Just as a follow up:

This code generates the guard: https://github.com/vuejs/vue/blob/daed1e73557d57df244ad8d46c9afff7208c9a2d/src/compiler/codegen/events.js#L81

It starts with all modifier keys and removes any that are present. So if none are present then the guard generates this:

if (
  $event.ctrlKey ||
  $event.shiftKey ||
  $event.altKey ||
  $event.metaKey
) {
  return null
}

So if any modifier present, it does not trigger the handler.

[michalsnik]

Thanks @mokkabonna ! LGTM 👍