splice.js

var slice = Array.prototype.slice

var addListener = require("./add-listener.js")
var setNonEnumerable = require("./lib/set-non-enumerable.js");

module.exports = splice

// `obs.splice` is a mutable implementation of `splice()`
// that mutates both `list` and the internal `valueList` that
// is the current value of `obs` itself
function splice(index, amount) {
    var obs = this
    var args = slice.call(arguments, 0)
    var valueList = obs().slice()

    // generate a list of args to mutate the internal
    // list of only obs
    var valueArgs = args.map(function (value, index) {
        if (index === 0 || index === 1) {
            return value
        }

        // must unpack observables that we are adding
        return typeof value === "function" ? value() : value
    })

    valueList.splice.apply(valueList, valueArgs)
    // we remove the observs that we remove
    var removed = obs._list.splice.apply(obs._list, args)

    var extraRemoveListeners = args.slice(2).map(function (observ) {
        return typeof observ === "function" ?
            addListener(obs, observ) :
            null
    })
    extraRemoveListeners.unshift(args[0], args[1])
    var removedListeners = obs._removeListeners.splice
        .apply(obs._removeListeners, extraRemoveListeners)

    removedListeners.forEach(function (removeObservListener) {
        if (removeObservListener) {
            removeObservListener()
        }
    })

    setNonEnumerable(valueList, "_diff", [valueArgs])

    obs._observSet(valueList)
    return removed
}