add reactive array swap

I am writing a simple todo list component with:

Vue.component('todo-list', {
    props: ['todos'],
    template:
    `<ol>
        <li v-for="(td, ix) in todos">
            {{td}}
            <button title="delete"  @click="todos.splice(ix,1)">X</button>
            <button title="move up" @click="todos.swap(ix,ix-1)" v-show="ix>0">^</button>
        </li>
    </ol>`,
})

For this to work I need (in core/observer/array.js) something like:

Array.prototype.swap = function(x,y) {
  var t = this[x]
  this[x] = this[y]
  this[y] = t
}
const arrayProto = Array.prototype
export const arrayMethods = Object.create(arrayProto)

/**
 * Intercept mutating methods and emit events
 */
;[
  'push',
  'pop',
  'shift',
  'unshift',
  'splice',
  'swap', // added
  'sort',
  'reverse'
]

It works when I (lazily) fixed dist/vue.js, but did not run the tests. I think it is worth to add swap this way because notify() is run just once, am I wrong?

[HerringtonDarkholme]

Why not just write

Vue.swap = function(arr, x, y) {
   var origin = arr[x]
   arr[x] = arr[y]
   Vue.set(arr, y, origin)
}

https://jsfiddle.net/L92w2372/2/

updated for notification only once

[LinusBorg]

Quick question: notifications are for the whole todo list right? Single elements of the list do not have notifications of their own.

In this case, they are., as we are changing an array.

Therefor one could aggregate helpers like this in a plugin and have the core clean.

Contreibution welcome.

I will close this issue now, since I think we have come to an understanding that this won’t be added to core.